Method of producing exchange coupling film and method of producing magnetoresistive sensor by using exchange coupling film

ABSTRACT

A laminate structure includes an antiferromagnetic layer, a pinned magnetic layer, and a seed layer contacting the antiferromagnetic layer on a side opposite to pinned magnetic layer. The seed layer is constituted mainly by face-centered cubic crystals with (111) planes preferentially oriented. The seed layer is preferably non-magnetic. Layers including the antiferromagnetic layer, a free magnetic layer, and layers therebetween, have (111) planes preferentially oriented.

This application is a division of application Ser. No. 09/833,306, filedApr. 11, 2001, now U.S. Pat. No. 6,648,985, which is hereby incorporatedby reference herein.

BACKGROUND

The present invention relates to methods of producing an exchangecoupling film having an antiferromagnetic layer and a ferromagneticlayer, wherein the direction of magnetization of the ferromagnetic layeris fixed by an exchange coupling magnetic field produced at theinterface between the antiferromagnetic layer and the ferromagneticlayer. More particularly, the present invention relates to methods ofproducing an exchange coupling film that provides a large ratio ofresistance variation, to methods of producing a magnetoresistive sensor(spin-valve-type thin-film device, AMR device), and to methods ofproducing a thin-film magnetic head using the magnetoresistive sensor.

DESCRIPTION OF THE RELATED ART

A spin-valve-type thin-film device is a kind of GMR (GiantMagnetoresistive) device which makes use of a giant magnetoresistiveeffect, which is used for detecting recording magnetic fields from arecording medium such as a hard disk.

The spin-valve-type thin-film device, relative to other GMR devices, hasadvantageous features such as simplicity of structure and ability tovary its magnetic resistance even under a weak magnetic field.

The simplest form of the spin-valve-type thin-film device includes anantiferromagnetic layer, a pinned magnetic layer, a non-magneticintermediate layer, and a free magnetic layer.

The antiferromagnetic layer and the pinned magnetic layer are formed incontact with each other. The direction of the pinned magnetic layer isaligned in a single magnetic domain state and fixed by an exchangeanisotropic magnetic field produced at the interface between theantiferromagnetic layer and the pinned magnetic layer.

The magnetization of the free magnetic layer is aligned in a directionwhich intersects the direction of magnetization of the pinned magneticlayer, by the effect of bias layers that are formed on both sides of thefree magnetic layer.

Alloy films such as Fe—Mn (Iron—Manganese) alloy films, Ni—Mn(Nickel—Manganese) alloy films, and Pt—Mn (Platinum—Manganese) alloyfilms are generally usable materials for the antiferromagnetic layer. Ofthese, Pt—Mn alloy films are attracting attention for advantages such asa high blocking temperature, superior corrosion resistance, and soforth.

In order to comply with future demand for higher recording density, itis important to achieve greater exchange coupling magnetic fields andgreater ratios of resistance variation.

However, it has been impossible to obtain a large ratio of resistancevariation with conventional structures of magnetoresistive sensors,which are composed of an antiferromagnetic layer, a pinned magneticlayer, a non-magnetic intermediate layer and a free magnetic layer.

It has been found that the ratio of resistance variation is dependent onexchange coupling magnetic field. The resistance variation ratiodecreases unless a large exchange coupling magnetic field is obtained.The resistance variation ratio is also dependent on the crystallineorientations of the layers. It has been heretofore impossible to useconventional structures to obtain a magnetoresistive sensor whichpossesses both appropriate crystalline orientations and a large exchangemagnetic field, and which therefore exhibits a large resistancevariation ratio.

SUMMARY

Accordingly, an object of the present invention is to provide methods ofproducing an exchange coupling film in which a seed layer is provided onthe side of an antiferromagnetic layer opposite to the interface betweenthe antiferromagnetic layer and the ferromagnetic layer, so as tooptimize the crystalline orientations of these layers. Thus, a greaterresistance variation ratio than obtained with conventional devices isachieved. Additional objects are to provide methods of producing amagnetoresistive sensor using the exchange coupling film, and methods ofproducing a thin-film magnetic head using the magnetoresistive sensor.In accord with the present invention, the above-described problems areovercome.

In accord with the present invention, there is provided a method ofproducing an exchange coupling film comprising an antiferromagneticlayer, a ferromagnetic layer contacting the antiferromagnetic layer atan interface therebetween, and a seed layer comprising a (111) plane offace-centered cubic crystal, which seed layer contacts theantiferromagnetic layer at an interface therebetween on a side oppositethe ferromagnetic layer. The method comprises forming the seed layersuch that the (111) plane of face-centered cubic crystal ispreferentially oriented in a direction parallel to the direction of theinterface between the seed layer and the antiferromagnetic layer, whilecreating a non-aligned state at at least a part of the interface betweenthe antiferromagnetic layer and the seed layer. The method furthercomprises effecting a heat-treatment after formation of the layers, soas to develop an exchange coupling magnetic field at the interfacebetween the antiferromagnetic layer and the ferromagnetic layer.

As stated above, in accordance with the present invention, a seed layercontacts the antiferromagnetic layer on a side thereof opposite theinterface between the antiferromagnetic layer and the ferromagneticlayer. The layer is constituted mainly by a face-centered cubiccrystalline structure in which, prior to heat treatment, the (111) planeis preferentially oriented in a direction parallel to the interface.This allows the (111) plane of the antiferromagnetic layer in contactwith the seed layer, and the (111) plane of the ferromagnetic layerwhich, together with the seed layer, sandwhiches the antiferromagneticlayer, to be preferentially oriented in a direction parallel to theinterface.

It is possible to enhance the resistance variation ratio of amagnetoresistive sensor by using an exchange coupling film in which the(111) planes of the antiferromagnetic layer and the ferromagnetic layerare preferentially oriented, as described above.

The enhancement of the resistance variation ratio requires that a largeexchange-coupling magnetic field be developed at the interface betweenthe antiferromagnetic layer and the ferromagnetic layer. In accordancewith the present invention, at least a part of the interface between thelayers is executed such that a non-aligned state is created at at leasta part of the interface between the antiferromagnetic layer and the seedlayer. Such a non-aligned state of the interface between the seed layerand the antiferromagnetic layer permits the antiferromagnetic layer tobe adequately transformed from a disordered lattice into an orderedlatticeupon heat-treatment. As a result, a large exchange couplingmagnetic field and, therefore, an enhanced resistance variation ratiocan be achieved.

The present invention also provides a method of producing an exchangecoupling film comprising an antiferromagnetic layer, a ferromagneticlayer contacting the antiferromagnetic layer at an interfacetherebetween, and a seed layer comprising a (111) plane of face-centeredcubic crystal, which seed layer contacts the antiferromagnetic layer atan interface therebetween on a side opposite the ferromagnetic layer,the method comprising forming the seed layer such that the (111) planeof face-centered cubic crystal is preferentially oriented in a directionparallel to the direction of the interface between the seed layer andthe antiferromagnetic layer, while creating a difference in latticeconstant between the antiferromagnetic layer and the seed layer at atleast a part of the interface therebetween. The method further compriseseffecting a heat-treatment after formation of the layers, so that anexchange coupling magnetic field is developed at the interface betweenthe antiferromagnetic layer and the ferromagnetic layer.

In accordance with the present invention, the antiferromagnetic layerand the ferromagnetic layer have different lattice constants at at leastapart of the interface between the antiferromagnetic layer and the seedlayer. Preferably, a non-aligned state is created at at least a part ofthe interface between the antiferromagnetic layer and the seed layer.These features make it possible to obtain a large exchange couplingmagnetic field and, hence, a large resistance variation ratio.

In accordance with the present invention, the antiferromagnetic layerpreferably comprises an element X and Mn, wherein the element X isselected from the group consisting of Pt, Pd, Ir, Rh, Ru, Os, andcombinations thereof.

Alternatively, the antiferromagnetic layer may comprise an element X, anelement X′ and Mn, wherein the element X is selected from the groupconsisting of Pt, Pd, Ir, Rh, Ru, Os, and combinations thereof, whilethe element X′ is selected from the group consisting of Ne, Ar, Kr, Xe,Be, B, C, N, Mg, Al, Si, P, Ti, V, Cr, Fe, Co, Ni, Cu, Zn, Ca, Ge, Zr,Nb, Mo, Ag, Cd, Sn, Hf, Ta, W, Re, Au, Pb, a rare earth element, andcombinations thereof.

The present invention also provides methods of producing an exchangecoupling film comprising an antiferromagnetic layer, a ferromagneticlayer contacting the antiferromagnetic layer at an interfacetherebetween, and a seed layer comprising a (111) plane of face-centeredcubic crystal, which seed layer contacts the antiferromagnetic layer atan interface therebetween on a side opposite the ferromagnetic layer,the method comprising: forming the seed layer such that the (111) planeof face-centered cubic crystal is preferentially oriented in a directionparallel to the interface between the seed layer and theantiferromagnetic layer; depositing on the seed layer anantiferromagnetic layer comprising an element X and Mn, wherein X isselected from the group consisting of Pt, Pd, Ir, Rh, Ru, Os, andcombinations thereof; elevating a sputtering gas pressure during thedepositing so that a composition ratio (at %) of the element X in theantiferromagnetic layer progressively decreases as distance from theseed layer increases; decreasing the sputtering gas pressure during thedepositing so that the composition ratio (at %) of the element X of theantiferromagnetic layer progressively increases as distance from theseed layer further increases; and effecting a heat-treatment afterformation of the layers, so as to develop an exchange coupling magneticfield at the interface between the antiferromagnetic layer and theferromagnetic layer.

The present invention also provides a method of producing an exchangecoupling film comprising an antiferromagnetic layer, a ferromagneticlayer contacting the antiferromagnetic layer at an interfacetherebetween, and a seed layer comprising a (111) plane offace-centerered cubic crystal, which seed layer contacts theantiferromagnetic layer at an interface therebetween on a side oppositeto ferromagnetic layer, the method comprising: forming the seed layersuch that the (111) plane of face-centered cubic crystal ispreferentially oriented in a direction parallel to the interface betweenthe seed layer and the antiferromagnetic layer; depositing on the seedlayer an antiferromagnetic layer comprising an element X, an element X′and Mn, wherein X is selected from the group consisting of Pt, Pd, Ir,Rh, Ru, Os, and combinations thereof, and X′ is selected from the groupconsisting of Ne, Ar, Kr, Xe, Be, B, C, N, Mg, Al, Si, P, Ti, V, Cr, Fe,Co, Ni, Cu, Zn, Ga, Ge, Zr, Nb, Mo, Ag, Cd, Sn, Hf, Ta, W, Re, Au, Pb, arare earth element, and combinations thereof; elevating a sputtering gaspressure during the depositing so that a composition ratio (at %) of theelements X+X′ of the antiferromagnetic layer progressively decreases asdistance from the seed layer increases; decreasing the sputtering gaspressure during the depositing so that the composition ratio (at %) ofthe elements X+X′ of the antiferromagnetic layer progressively increasesas distance from the seed layer further increases; and effecting aheat-treatment after formation of the layers, so as to develop anexchange coupling magnetic field at the interface between theantiferromagnetic layer and the ferromagnetic layer.

According to this method of the present invention, a portion of acomposition prone to order transformation is formed near the middle ofthe antiferromagnetic layer. The antiferromagnetic layer is formed suchthat the composition of the antiferromagnetic layer at the interfacebetween the seed layer and the antiferromagnetic layer is notconstrained by factors such as the crystalline structure of the seedlayer.

In these methods of the present invention, the composition ratio of theelement X or the composition ratio of the elements X+X′ of theantiferromagnetic layer to the total composition ratio (100 at %) of allthe elements constituting the antiferromagnetic layer is not less than53 at % and not more than 65 at %, preferably not less than 55 at % andnot more than 60 at %, in a region near the interface between theantiferromagnetic layer and the ferromagnetic layer, and in a regionnear the interface between the antiferromagnetic layer and the seedlayer.

In these methods of the present invention, it is also preferred that thecomposition ratio of the element X or the composition ratio of theelements X+X′ is not less than 44 at % and not more than 57 at %, morepreferably not less than 46 at % and not more than 55 at %, in a regionnear the thicknesswise central portion of the antiferromagnetic layer.

Preferably, the antiferromagnetic layer is formed to have a thickness of76 Å or greater.

The present invention also provides a method of producing an exchangecoupling film comprising an antiferromagnetic layer, a ferromagneticlayer contacting the antiferromagnetic layer at an interfacetherebetween, and a seed layer comprising a (111) plane of face-centeredcubic crystal, which seed layer contacts the antiferromagnetic layer atan interface therebetween on a side opposite to the ferromagnetic layer,the antiferromagnetic layer comprising a first antiferromagnetic layer,a second antiferromagnetic layer, and a third antiferromagnetic layer,the method comprising: forming the seed layer such that the (111) planeof face-centered cubic crystal is preferentially oriented in a directionparallel to the interface between the seed layer and theantiferromagnetic layer; forming the antiferromagnetic layer such thatthe third antiferromagnetic layer is adjacent to the seed layer, thefirst antiferromagnetic layer is adjacent to the ferromagnetic layer,and the second antiferromagnetic layer is between the first and thirdantiferromagnetic layers, wherein each of the first, the second, and thethird antiferromagnetic layers comprises an element X and Mn, wherein Xis selected from the group consisting of Pt, Pd, Ir, Rh, Ru, Os, andcombinations thereof, such that the second antiferromagnetic layer has asmaller composition ratio of the element X than the first and the secondantiferromagnetic layers; and effecting a heat-treatment after formationof the layers, such that an exchange coupling magnetic field isdeveloped at the interface between the antiferromagnetic layer and theferromagnetic layer.

In this method of the present invention, the first, second and thirdantiferromagnetic layers may be formed from antiferromagnetic materialscomprising an element X, an element X′ and Mn, wherein the element X′ isselected from the group consisting of Ne, Ar, Kr, Xe, Be, B, C, N, Mg,Al, Si, P, Ti, V, Cr, Fe, Co, Ni, Cu, Zn, Ga, Ge, Zr, Nb, Mo, Ag, Cd,Sn, Hf, Ta, W, Re, Au, Pb, a rare earth element, and combinationsthereof.

In this method of the present invention, the antiferromagnetic layer iscomposed of a triple-layer laminate. During deposition of the thirdantiferromagnetic layer, the composition ratio of the element X in thethird antiferromagnetic layer is set to be greater than that of thesecond antiferromagnetic layer so that, at the interface between thethird antiferromagnetic layer and the seed layer, the restraint forceproduced by the crystalline structure of the seed layer is weakened. Asa result, a non-aligned state or a different lattice constant isobtained, thereby facilitating transformation of the antiferromagneticlayer to an ordered lattice upon heat-treatment without influence fromthe crystalline structure of the seed layer. As a result, a greaterexchange coupling magnetic field is obtained than heretofore.

Setting the composition ratio of the element X in the secondantiferromagnetic layer to a value smaller than in the first and thirdantiferromagnetic layers facilitates transformation of the secondantiferromagnetic layer upon heat-treatment. This in turn promotestransformation of the whole antiferromagnetic layer through a diffusionof the composition, whereby a large exchange coupling magnetic field isobtained.

In accordance with the present invention, the antiferromagnetic layerand the seed layer may have different lattice constants at at least apart of the interface therebetween. Preferably, in accord with thepresent invention, a non-aligned state is created at at least a part ofthe interface between the antiferromagnetic layer and the seed layer.

When the above-mentioned X—Mn—X′ alloy is used as the material of theantiferromagnetic layer, it is preferred that the element X′ is anelement which either invades the interstices of a space lattice composedof the element X and Mn, or substitutes for a portion of the latticepoints of a crystalline lattice constituted by Mn and the element X.

In accordance with the present invention, the composition ratio of theelement X or the composition ratio of the elements X+X′ of each of thefirst and third antiferromagnetic layers is preferably not less than 53at % and not more than 65 at %, more preferably not less than 55 at %and not more than 60 at %.

In accordance with the present invention, it is also preferred that thecomposition ratio of the element X or the composition ratio of theelements X+X′ of the second antiferromagnetic layer is not less than 44at % and not more than 57 at%, more preferably not less than 46 at % butnot more than 55 at %.

In accordance with the present invention, it is preferred that each ofthe first and third antiferromagnetic layers has a thickness not smallerthan 3 Å and not greater than 30 Å.

In accordance with the present invention, it is also preferred that thesecond antiferromagnetic layer has a thickness of 70 Å or greater.

In accordance with the present invention, it is preferred that theantiferromagnetic layer and the ferromagnetic layer have differentlattice constants at at least a part of the interface therebetween. Inaddition, it is preferred that a non-aligned state is created at atleast a part of the above-mentioned interface. With these features, anappropriate ordered transformation of the entire antiferromagnetic layeris facilitated.

In accordance with the present invention, it is preferred that the seedlayer is formed of a Ni—Fe alloy or a Ni—Fe—Y alloy, wherein Y isselected from the group consisting of Cr, Rh, Ta, Hf, Nb, Zr, Ti, andcombinations thereof.

It is also preferred that the seed layer is non-magnetic. Thenon-magnetic nature of the seed layer serves to enhance the specificresistance of the seed layer, so that shunting of a sense current to theseed layer is suppressed. As a result, greater resistance variationratio in the exchange coupling film obtained after heat-treatment isobtained.

In accordance with the present invention, it is preferred that theexchange coupling film is formed by sequentially depositing a seedlayer, an antiferromagnetic layer, and a ferromagnetic layer on anunderlying layer, wherein the underlying layer comprises an elementselected from the group consisting of Ta, Hf, Nb, Zr, Ti, Mo, W, andcombinations thereof.

This facilitates formation of a seed layer having a crystallinestructure constituted mainly by face-centered cubic crystals with the(111) plane preferentially oriented in a direction parallel to theabove-mentioned interface.

The methods of producing an exchange coupling film described hereinabovecan be used for the production of a variety of types of magnetoresistivesensors.

In accordance with the present invention, there is provided a method ofproducing a magnetoresistive sensor comprising an antiferromagneticlayer, a seed layer contacting the antiferromagnetic layer at aninterface therebetween, a pinned magnetic layer contacting theantiferromagnetic layer at an interface therebetween which has adirection of magnetization fixed by an exchange anisotropic magneticfield with the antiferromagnetic layer, a non-magnetic intermediatelayer between the pinned magnetic layer and a free magnetic layer, and abias layer which aligns a direction of magnetization of the freemagnetic layer in a direction that intersects the direction ofmagnetization of the pinned magnetic layer, the method comprisingforming the antiferromagnetic layer, the pinned magnetic layer, and theseed layer by one of the methods described hereinabove.

In accordance with the present invention, there is provided a method ofproducing a magnetoresistive sensor comprising an antiferromagneticlayer, a seed layer contacting the antiferromagnetic layer at aninterface therebetween, a pinned magnetic layer contacting theantiferromagnetic layer at an interface therebetween which has adirection of magnetization fixed by an exchange anisotropic magneticfield with the antiferromagnetic layer, a non-magnetic intermediatelayer between the pinned magnetic layer and a free magnetic layer havingan upper side and a lower side, and an antiferromagnetic exchange biaslayer formed on either the upper side or the lower side of the freemagnetic layer, the antiferromagnetic exchange bias layer comprising atleast one gap in the track width direction, the method comprising:forming the exchange bias layer, the free magnetic layer and the seedlayer by one of the methods described hereinabove.

The present invention also provides a method of producing amagnetoresistive sensor comprising a seed layer; a firstantiferromagnetic layer overlying the seed layer; a first pinnedmagnetic layer overlying the first antiferromagnetic layer; a firstnon-magnetic layer overlying the first pinned magnetic layer; a freemagnetic layer overlying the first non-magnetic layer, the free magneticlayer having an upper side and a lower side; a second non-magnetic layeroverlying the free magnetic layer; a second pinned magnetic layeroverlying the second non-magnetic layer; a second antiferromagneticlayer overlying the second pinned magnetic layer, the first and secondantiferromagnetic layers serving to fix directions of magnetization ofthe first and the second pinned magnetic layers by exchange anisotropicmagnetic fields; and a bias layer which aligns a direction ofmagnetization of the free magnetic layer to a direction that intersectsthe directions of the first and the second pinned magnetic layers, themethod comprising: forming at least one of the first and the secondantiferromagnetic layers, at least one of the first and the secondpinned magnetic layers, the seed layer and at least one of the lowerside and the upper side of the free magnetic layer, by one of themethods described hereinabove.

The present invention also provides a method of producing amagnetoresistive sensor comprising a magnetoresistive layer having anupper side and a lower side and a soft magnetic layer, themagnetoresistive layer and the soft magnetic layer being superposedthrough the intermediacy of a non-magnetic layer, an antiferromagneticlayer on the upper side or the lower side of the magnetoresistive layer,the antiferromagnetic layer comprising at least one gap in the trackwidth direction, and a seed layer contacting the antiferromagneticlayer, the method comprising the forming the antiferromagnetic layer,the magnetoresistive layer and the seed layer by one of the methodsdescribed hereinabove.

A method for producing a thin-film magnetic head in accord with thepresent invention comprises forming a shield layer across the gap layer,on each of the upper side and the lower side of a magnetoresistivesensor produced by one of the methods described hereinabove.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a sectional view of a single-spin valve type magnetoresistivesensor in accord with the present invention, viewed from the same sideas an ABS surface.

FIG. 2 is a schematic illustration of a laminate structure in accordwith the present invention in a state after deposition and prior toheat-treatment.

FIG. 3 is a schematic illustration of the laminate structure of FIG. 2in a state after heat-treatment.

FIG. 4 is a schematic illustration of a laminate structure having a seedlayer in accord with the present invention, in a state after depositionand prior to heat-treatment.

FIG. 5 is a schematic illustration of the laminate structure of FIG. 4in a state after heat-treatment.

FIG. 6 is a sectional view of a single-spin valve type magnetoresistivesensor in accord with the present invention, viewed from the same sideas an ABS surface.

FIG. 7 is a sectional view of a single-spin valve type magnetoresistivesensor in accord with the present invention, viewed from the same sideas an ABS surface.

FIG. 8 is a sectional view of a single-spin valve type magnetoresistivesensor in accord with the present invention, viewed from the same sideas an ABS surface.

FIG. 9 is a sectional view of a single-spin valve type magnetoresistivesensor in accord with the present invention, viewed from the same sideas an ABS surface.

FIG. 10 is a schematic illustration of a dual-spin valve type laminatestructure in a state after deposition.

FIG. 11 is a schematic illustration of the laminate structure of FIG. 10in a state after heat-treatment.

FIG. 12 is a schematic illustration of a dual-spin valve type laminatestructure having a seed layer, in a state after deposition.

FIG. 13 is a schematic illustration of the laminate structure of FIG. 12in a state after heat-treatment.

FIG. 14 is a sectional view of an AMR magnetoresistive sensor in accordwith the present invention, viewed from the same side as the ABSsurface.

FIG. 15 is a sectional view of an AMR magnetoresistive sensor in accordwith the present invention, viewed from the same side as the ABSsurface.

FIG. 16 is a fragmentary sectional view of a thin-film magnetic head(reproduction head) in accord with the present invention.

FIG. 17 is a graph showing the relationship between exchange couplingmagnetic field (Hex) and total film thickness of an antiferromagneticlayer formed from a first antiferromagnetic layer and a secondantiferromagnetic layer.

FIG. 18 is a graph showing the relationship between exchange couplingmagnetic field (Hex), and the thickness of a first antiferromagneticlayer which, together with a second antiferromagnetic layer, forms anantiferromagnetic layer.

FIG. 19 is a graph showing the relationship between Pt content (x) andexchange coupling magnetic field (Hex) in a structure having anantiferromagnetic layer composed of a first antiferromagnetic layer anda second antiferromagnetic layer, the first antiferromagnetic layerhaving a composition expressed by Pt_(x)Mn_(100−x).

FIG. 20 is a schematic illustration a conventional single-spin valvetype magnetoresistive sensor.

FIG. 21 is a schematic illustration of a conventional experimentalsingle-spin valve type magnetoresistive sensor having a seed layer.

DESCRIPTION OF THE PRESENTLY PREFERRED EMBODIMENTS

FIG. 1 is a sectional view of a single-spin valve type magnetoresistivesensor constituting a first embodiment of the present invention, viewedfrom the same side as the ABS surface. In FIG. 1, only the centralportion of the device extending in the X direction is shown.

This single-spin valve type magnetoresistive sensor can be provided on atrailing side end of a floating slider of a hard disk device, and can beused to detect the recording magnetic fields of the hard disk. Arecording medium such as the hard disk moves in the Z direction, whilethe magnetic field leaks from the hard disk in the Y direction.

Referring to FIG. 6, the lowermost layer, underlying layer 6, is madefrom a non-magnetic material containing one or more elements selectedfrom the group consisting of Ta, Hf, Nb, Zr, Mo, and W. A free magneticlayer 1, a non-magnetic intermediate layer 2, a pinned magnetic layer 3,and an antiferromagnetic layer 4 are deposited on underlying layer 6. Aprotective layer 7 made from a non-magnetic material containing one ormore elements selected from the group consisting of Ta, Hf, Nb, Zr, Ti,Mo, and W overlies antiferromagnetic layer 4.

As shown in FIG. 1, a hard bias layer 5 is formed on each end of thesix-layered laminate composed of six layers from underlying layer 6 toprotective layers 7 inclusive. A conductive layer 8 is deposited on eachportion of the hard bias layer 5.

In accordance with the present invention, each of free magnetic layer 1and pinned magnetic layer 3 is made from, for example, a Ni—Fe alloy, aCo—Fe alloy, Co, or a Co—Ni—Fe alloy.

In the structure shown in FIG. 1, the free magnetic layer 1 is formedfrom a single layer. However, free magnetic layer 1 may alternatively bemulti-layered. For instance, free magnetic layer 1 may be formed of alaminate composed of layers of a Ni—Fe alloy and Co.

The non-magnetic intermediate layer 2 interposed between free magneticlayer 1 and pinned magnetic layer 3 is formed of Cu, for example. Whenthe magnetoresistive sensor embodying the present invention is atunnel-type magnetoresistive sensor (TMR sensor) which uses thetunneling effect, the non-magnetic intermediate layer 2 is made from aninsulating material such as Al₂O₃. The hard bias layer 5 is formed of,for example, a Co—Pt (cobalt—platinum) alloy or a Co—Cr—Pt(cobalt—chromium—platinum) alloy. The conductive layer 8 is made fromCu, W, or the like. In the case of a tunnel-type magnetoresistivesensor, the conductive layer 8 is formed on both the lower side of thefree magnetic layer 1 and the upper side of the antiferromagnetic layer4.

A method of producing a magnetoresistive sensor in accord with thepresent invention, will be described, followed by a description of thefeatures of the magnetoresistive sensor produced.

FIG. 2 is a schematic illustration of a laminate structure which has,analogous to the structure shown in FIG. 1, a lowermost underlying layer6 and an uppermost protective layer 7, with an antiferromagnetic layer 4formed on the upper side of a pinned magnetic layer 3. The laminatestructure shown in FIG. 2 is in a state after deposition and prior toheat-treatment.

Initially, underlying layer 6 of Ta or the like is formed on a substrate(not shown). By way of example, the underlying layer 6 is formed to havea thickness of 50 Å or so.

By way of example, a Ni—Fe alloy film 9 is formed on the underlyinglayer 6, and a Co film 10 is formed on the Ni—Fe alloy film 9. The Ni—Fealloy film 9 and the Co film 10 together form free magnetic layer 1. Byforming Co film 10 on the side of the free magnetic layer 1 thatcontacts non-magnetic intermediate layer 2, it is possible to preventdiffusion of the metal elements at the interface between free magneticlayer 1 and non-magnetic intermediate layer 2 and, therefore, toincrease the resistance variation ratio ΔMR.

The Ni—Fe alloy film 9 is formed to contain, for example, 80 at % of Niand 20 at % of Fe. The Ni—Fe alloy film 9 has a thickness of about 45 Å,while the Co film 10 has a thickness of about 5 Å.

Non-magnetic intermediate layer 2 formed, for example, of Cu overliesfree magnetic layer 1. By way of example, non-magnetic intermediatelayer 2 has a film thickness of about 25 Å.

Pinned magnetic layer 3 is formed on non-magnetic intermediate layer 2.In this embodiment, pinned magnetic layer 3 is composed of atriple-layered laminate structure.

By way of example, pinned magnetic layer 3 is composed of a first Cofilm 11, a Ru film 12, and a second Co film 13. Due to the exchangecoupling magnetic field acting at the interface between pinned magneticlayer 3 and antiferromagnetic layer 4 (described below), Co film 11 andthe Co film 13 are made to have directions of magnetization that are notparallel. This state is generally referred to as a ferromagnetic state,and it serves to stabilize the magnetization of pinned magnetic layer 3,while providing a greater exchange coupling magnetic field at theinterface between pinned magnetic layer 3 and antiferromagnetic layer 4.

The Co film 11 is formed to have a thickness of about 20 Å, Ru film 12is formed to have a thickness of about 8 Å, and Co film 13 is formed tohave a thickness of about 15 Å.

Antiferromagnetic layer 4 is formed on pinned magnetic layer 3. As shownin FIG. 3, a first antiferromagnetic layer 14 is formed on the pinnedmagnetic layer 3, and a second antiferromagnetic layer 15 is formed onthe first antiferromagnetic layer 14.

In accordance with the present invention, each of the firstantiferromagnetic layer 14 and the second antiferromagnetic layer 15 maybe formed from an antiferromagnetic material which contains an element Xand Mn, wherein X is one or more elements selected from the groupconsisting of Pt, Pd, Ir, Rh, Ru, and Os.

X—Mn alloys containing one or more platinum-group elements exhibitsuperior corrosion resistance and high blocking temperature, as well assuperior properties required for antiferromagnetic materials, such as aa large exchange coupling magnetic field (Hex). Among the platinum groupelements, Pt is preferred in the form, for example, of a binary-systemPt—Mn alloy.

In accordance with the present invention, each of the firstantiferromagnetic layer 14 and the second antiferromagnetic layer 15 mayalso be formed from an antiferromagnetic material which contains anelement X, an element X′ and Mn, wherein the element X′ is one or moreelements selected from the group consisting of Ne, Ar, Kr, Xe, Be, B, C,N, Mg, Al, Si, P, Ti, V, Cr, Fe, Co, Ni, Cu, Zn, Ga, Ge, Zr, Nb, Mo, Ag,Cd, Sn, Hf, Ta, W, Re, Au, Pb and a rare earth element.

Preferably, the element X′ is an element which invades the intersticesof the space lattice constituted by the element X and Mn, or an elementwhich substitutes for a portion of the lattice points of a crystallinelattice formed by the element X and Mn. The term “solid solution” asused herein means a solid in which components are uniformly mixed over awide region.

The formation of an interstitial solid solution or a substitutionalsolid solution enables the lattice constant of the X—Mn—X′ alloy to begreater than the lattice constant of the aforementioned X—Mn alloy,which results in a larger difference in lattice constant relative to thelattice constant of the pinned magnetic layer 3, thereby facilitatingcreation of a non-aligned state at the interface betweenantiferromagnetic layer 4 and pinned magnetic layer 3. When the elementX′ forms a substitutional solid solution, too large of a compositionratio of the element X′ will impair the antiferromagnetic properties,resulting in a smaller exchange coupling magnetic field at the interfacebetween pinned magnetic layer 3 and antiferromagnetic layer 4. Inaccordance with the present invention, therefore, it is preferred thatan inert rare gas element (one or more of Ne, Ar, Kr, and Xe) whichforms an interstitial solid solution be used as the element X′. The raregas element is inert, and does not significantly affect theantiferromagnetic properties even when it is present in the film. Inaddition, Ar is a gas conventionally used as a sputter gas in asputtering apparatus and, therefore, can be easily contained in thefilm.

When the element X′ is a gaseous element, it is difficult to incorporatea large amount of it in the film. However, a trace amount of a rare gaselement X′ drastically increases the exchange coupling magnetic fieldgenerated upon heat-treatment.

In accordance with the present invention, the composition ratio of theelement X′ preferably ranges from 0.2 at % to 10 at %, more preferablyfrom 0.5 at % to 5 at %. In accordance with the present invention, it ispossible to use Pt as the element X and, hence, to use a Pt—Mn—X′ alloy.

The element X and elements X+X′ which form the first antiferromagneticlayer 14 and the antiferromagnetic layer 15 may be the same ordifferent. For instance, it is possible to use a Pt—Mn—X′ alloy toprovide a large lattice constant as the material for the firstantiferromagnetic layer 14, and a Pt—Mn as the material for the secondantiferromagnetic layer 15.

In the laminate structure after deposition (prior to heat-treatment)shown in FIG. 2, it is important that the composition ratio (at %) ofelement X in the first antiferromagnetic layer 14 be greater than thecomposition ratio (at %) of the element X in the secondantiferromagnetic layer 15. When each of the first antiferromagneticlayer 14 and the second antiferromagnetic layer 15 is made from anX—Mn—X′ alloy, the composition ratio (at %) of the elements X+X′ in thefirst antiferromagnetic layer 14 is determined to be greater than thecomposition ratio (at %) of the elements X+X′ in the secondantiferromagnetic layer 15. When the first antiferromagnetic layer 14 ismade of an X—Mn—X′ alloy and the second antiferromagnetic layer 15 ismade of an X—Mn alloy, the composition ratio (at %) of the elements X+X′in the first antiferromagnetic layer 14 is determined to be greater thanthe composition ratio (at %) of the element X in the secondantiferromagnetic layer 15.

After the second antiferromagnetic layer 15 has been deposited in thefirst antiferromagnetic layer 14 and a heat-treatment has beenconducted, first antiferromagnetic layer 14 weakens the restraint forceof the crystalline structure of pinned magnetic layer 3, such that thesecond antiferromagnetic layer 15 is kept away from the restraint force,and the disordered lattice of antiferromagnetic layer 14 can be properlytransformed into an ordered lattice.

In order to reduce the influence of the restraint force produced by thecrystalline structure of pinned magnetic layer 3 at the interfacebetween antiferromagnetic layer 4 and pinned magnetic layer 3, it isnecessary that the composition ratio of element X or elements X+X′ inthe first antiferromagnetic layer be sufficiently large.

A large composition ratio of the element X or elements X+X′ reduces thetendency of the composition to form an ordered lattice uponheat-treatment, but increases the difference in lattice constantsrelative to the pinned magnetic layer. Increased differences in latticeconstants reduces the influence of the restraint force produced by thecrystalline structure of pinned magnetic layer 3 on the firstantiferromagnetic layer 14 and, hence, on the second antiferromagneticlayer 15.

In accordance with the present invention, it is preferred that anon-aligned state is created at part of the interface between the firstantiferromagnetic layer 14 and the pinned magnetic layer 3. The presenceof a non-aligned state at this interface further reduces the influenceof the crystalline structure of pinned magnetic layer 3 on firstantiferromagnetic layer 14.

As noted above, in a bulk type Pt—Mn alloy, a CuAu—I type face-centeredcubic ordered lattice is easiest to obtain—and, therefore,antiferromagnetic properties are easiest to achieve—when the at % ratiobetween Pt and Mn is 50:50. Increasing the Pt content beyond 50 at %weakens the antiferromagnetic properties on the one hand, but increasesthe lattice constant of the Pt—Mn alloy on the other, therebyfacilitating creation of non-aligned state at the interface between thepinned magnetic layer 3 and the antiferromagnetic layer 4.

Preferably, the composition ratio of the element X or the elements X+X′of the first antiferromagnetic layer 14 is not less than 53 at % and notgreater than 65 at %. More preferably, this composition ratio is notless than 55 at % and not greater than 60 at %. Results of experimentswhich will be described hereinbelow show that an exchange couplingmagnetic field of 7.9×10⁴ A/m or greater is obtainable with suchcomposition ratios.

It is to be understood that there are preferred thicknesses for thefirst antiferromagnetic layer 14. Too small a thickness weakens thenon-aligned state at the interface between the first antiferromagneticlayer 14 and the pinned magnetic layer 3, making it impossible to obtaina proper intensity of exchange coupling magnetic field uponheat-treatment. The first antiferromagnetic layer 14 has a compositionwhich inherently is not liable to transform from a disordered latticeinto an ordered lattice and, hence, is less liable to possessantiferromagnetic properties upon heat-treatment. As a result, too largea thickness of first antiferromagnetic layer 14 increases the proportionof the region that is hard to transform, which in turn increases theregion which remains disordered after heat-treatment, therebydrastically reducing the exchange coupling magnetic field.

In accordance with the present invention, the thickness of the firstantiferromagnetic layer 14 is preferably not smaller than 3 Å and notgreater than 30 Å. Results of experiments described below show that athickness of the first antiferromagnetic layer 14 within theabove-specified range provides a large exchange coupling magnetic field(Hex), specifically an exchange coupling magnetic field of 7.9×10⁴ A/mor greater.

A second antiferromagnetic layer 15, which has a composition ratio ofthe element X or the elements X+X′ which is smaller than that of thefirst antiferromagnetic layer 14, is formed on the firstantiferromagnetic layer 14 after the deposition thereof.

Preferably, the composition ratio of the element X or the elements X+X′in the second antiferromagnetic layer 15 is not smaller than 44 at % andnot greater than 57 at %, more preferably not smaller than 46 at % andnot greater than 55 at %, and most preferably not smaller than 48 at %and not smaller than 53 at %.

It is also preferred that the composition ratio of the element X or theelements X+X′ in the second antiferromagnetic layer 15 approximates anideal composition ratio for causing transformation from a disorderedlattice into an ordered lattice upon heat-treatment, so thatheat-treatment executed after deposition of the second antiferromagneticlayer 15 causes the latter to properly transform its structure from adisordered lattice into an ordered lattice.

It is to be noted that there are preferred thicknesses of the secondantiferromagnetic layer 15. It has been confirmed through experimentthat too small a thickness of the second antiferromagnetic layer 15causes a drastic reduction in the exchange coupling magnetic field(Hex).

In accordance with the present invention, it is preferred that thesecond antiferromagnetic layer 15 has a thickness not smaller than 70 Å.A thickness meeting this requirement makes it possible to obtain a largeexchange coupling magnetic field, specifically 7.9×10⁴ A/m or greater.

In accordance with the present invention, it is preferred that the firstantiferromagnetic layer 14 and the second antiferromagnetic layer 15 areformed by a sputtering process.

In particular, when the first antiferromagnetic layer 14 or the secondantiferromagnetic layer 15 is formed of an X—Mn—X′ alloy, usingsputtering to deposit the alloy enables deposition of a non-equilibriumstate, so that the element X′ invades the interstices of the spacelattice constituted by the element X and Mn or substitutes for a portionof the lattice points of the crystalline lattice formed by the element Xand Mn. As a result of the formation of an interstitial solid solutionor a substitutional solid solution by the use of element X′, the latticeis expanded and the lattice constant of the antiferromagnetic layer 4 islarger than in the absence of the element X′.

In accordance with the present invention, the deposition of the firstantiferromagnetic layer 14 and the second antiferromagnetic layer by asputtering process is preferably conducted such that in the depositionof the first antiferromagnetic layer 14, the sputtering gas pressure ismaintained at a level lower than in the deposition of the secondantiferromagnetic layer 15. Such a technique provides a compositionratio of the element X or the elements X+X′ in the firstantiferromagnetic layer 14 which is greater than that in the secondantiferromagnetic layer 15.

Thus, in accordance with the present invention, it is preferred that theantiferromagnetic layer 4 has a laminate structure comprising the firstantiferromagnetic layer 14 and the second antiferromagnetic layer 15,the first and second antiferromagnetic layers 14 and 15 being depositedsuch that the composition ratio of the element X or the elements X+X′ inthe first antiferromagnetic layer 14 is greater than in the secondantiferromagnetic layer 15, such that the influence of the restraintforce produced by the crystalline structure of pinned magnetic layer 3on the first antiferromagnetic layer 14 at the interface between firstantiferromagnetic layer 14 and pinned magnetic layer 3 is reduced. Thus,a non-aligned state is created at at least a part of the interface,thereby enabling proper transformation from a disordered lattice into anordered lattice upon heat-treatment, and a large exchange couplingmagnetic field between antiferromagnetic layer 4 and pinned magneticlayer 3.

In accordance with the present invention, as noted above, it ispreferred that a non-aligned state is created at at least a part of theinterface between the first antiferromagnetic layer 14 and the pinnedmagnetic layer 3 following deposition of the layers. Such a non-alignedstate can be obtained by providing a first antiferromagnetic layer 14and a second antiferromagnetic layer 15 with different latticeconstants. It is sufficient to produce such a difference at only a partof the above-mentioned interface.

Alternatively, different crystal orientations are created at at least apart of the first antiferromagnetic layer 14 and the pinned magneticlayer 3. Creation of the above-mentioned non-aligned state at at least apart of the interface between the first antiferromagnetic layer 14 andthe pinned magnetic layer 3 can also be facilitated by employingdifferent crystal orientations.

For instance, when the (111) plane of pinned magnetic layer 3 has beenpreferentially oriented in a direction parallel to the film surface, the(111) plane of the first antiferromagnetic layer 14 is set to eitherhave a smaller degree of orientation than the (111) plane of pinnedmagnetic layer 3, or to be altogether unoriented.

Alternatively, when the (111) plane of the first antiferromagnetic layer3 has been preferentially oriented in a direction parallel to the filmsurface, the (111) plane of pinned magnetic layer 3 is either set tohave a smaller degree of orientation than the (111) plane of the firstantiferromagnetic layer 14, or the (111) plane of the firstantiferromagnetic layer 14 altogether unoriented.

Alternatively, the degrees of orientation of the (111) faces of firstantiferromagnetic layer 14 and pinned magnetic layer 3 are both reduced,or the faces are altogether unoriented, with respect to the directionsparallel to the interface between the first antiferromagnetic layer 14and pinned magnetic layer 3. The degree of crystal orientation iscontrollable by varying the order of deposition of the layers, or byvarying conditions such as presence or absence of an underlying layer,composition ratio, electrical power and gas pressure during sputtering.

The laminate structure thus formed is then subjected to aheat-treatment. As a result of heat-treatment, an exchange couplingmagnetic field is generated at the interface between theantiferromagnetic layer 4 and the pinned magnetic layer 3, so that themagnetization of pinned magnetic layer 3 is formed into a singlemagnetic domain in a predetermined direction, specifically in thevertical direction Y, as shown in FIG. 1.

As described above, the first antiferromagnetic layer 14 is notrestrained by the crystalline structure of pinned magnetic layer 3 atthe interface between first antiferromagnetic layer 14 and pinnedmagnetic layer 3. Preferably, a non-aligned state is created at at leasta part of the interface, so that the second antiferromagnetic layer 15formed on pinned magnetic layer 1 through the intermediary of the firstantiferromagnetic layer starts to transform from a disordered lattice toan ordered lattice while the above-mentioned non-aligned state ismaintained. This is because second antiferromagnetic layer 15 is formedfrom an antiferromagnetic material having a composition approximatingthe ideal composition for facile transformation from a disorderedlattice to an ordered lattice, as described above.

While it is not the Applicants' desire to be bound by a particulartheory, it is believed that diffusion of composition takes place at theinterface between first antiferromagnetic layer 14 and secondantiferromagnetic layer 15, once such a transformation is started. Suchdiffusion allows the elements of the second antiferromagnetic layer tomigrate into the first antiferromagnetic layer 14, and the elements ofthe first antiferromagnetic layer 14 to migrate into the secondantiferromagnetic layer 15, whereby an antiferromagnetic layer 4 withouta distinct border is formed, in which elements of both the firstantiferromagnetic layer 14 and the second antiferromagnetic layer 15 aremixed together.

While it is not the Applicants' desire to be bound by a particulartheory, it is believed that in the region near the interface betweenfirst antiferromagnetic layer 14 and second antiferromagnetic layer 15,the composition ratio (at %) of the element X or the elements X+X′ issmaller than that in the first antiferromagnetic layer 14 as initiallydeposited, due to the above-described diffusion. Consequently, when thesecond antiferromagnetic layer starts to be transformed into an orderedlattice upon heat-treatment, transformation is also promoted in thefirst antiferromagnetic layer. At the interface between the pinnedmagnetic layer and the antiferromagnetic layer 4, the firstantiferromagnetic layer is freed from the influence of the restraintforce of the crystalline structure of the pinned magnetic layer, wherebya transformation from a disordered lattice into an ordered lattice takesplace over the whole antiferromagnetic layer 4, and a greater exchangecoupling magnetic field than heretofore is achieved.

The laminate structure obtained after heat-treatment is shownschematically in FIG. 3. The configuration of the laminate structurefrom the lowermost underlying layer 6 to pinned magnetic layer 3 is notchanged by heat-treatment. However, the structure of antiferromagneticlayer 4 is changed from the structure as deposited (prior toheat-treatment, as in FIG. 2) to the structure shown in FIG. 3.

The antiferromagnetic layer 4 shown in FIG. 3 is formed from anantiferromagnetic material comprising an element X and Mn, where theelement X is one or more elements selected from the group consisting ofPt, Pd, Ir, Rh, Ru, and Os, or from an antiferromagnetic materialcomprising an element X, an element X′ and Mn, where the element X′ isone or more elements selected from the group consisting of Ne, Ar, Kr,Xe, Be, B, C, N, Mg, Al, Si, P, Ti, V, Cr, Fe, Co, Ni, Cu, Zn, Ga, Ge,Zr, Nb, Mo, Ag, Cd, Sn, Hf, Ta, W, Re, Au, Pb and a rare earth element.

Preferably, the aforementioned X—Mn—X′ alloy either has the form of aninterstitial solid solution in which the element X′ has enteredinterstices of the space lattice constituted by the element X and Mn, orthe form of a substitutional solid solution in which the element X′ hassubstituted for a portion of the lattice points of the crystal latticeformed of the element X and Mn. Thus, the X—Mn—X′ alloy can have anexpanded lattice constant over the X—Mn alloy, making it easier tocreate a non-aligned state at the interface between antiferromagneticlayer 4 and pinned magnetic layer after heat-treatment.

In accordance with the present invention, antiferromagnetic layer 4 hasa region in which the ratio of the atomic percent of element X orelements X+X′ to Mn increases towards pinned magnetic layer 3.

In addition, at least part of the crystalline structure ofantiferromagnetic layer 4 has a CuAu—I type face-centered cubic lattice(ordered lattice). Preferably, an unaligned state is created at at leasta part of the aforementioned interface A.

The reason for having a region in which the ratio of the atomic percentof element X or elements X+X′ to Mn increases towards pinned magneticlayer 3 is that the diffusion experienced by the first antiferromagneticlayer 14 and the second antiferromagnetic layer 15 is imperfect, and thefirst antiferromagnetic layer 14 and second antiferromagnetic layer arenot completely diffused in each other. Thus, the antiferromagnetic layerafter heat-treatment does not have a completely uniform structure.

As explained above in reference to FIG. 2, the composition ratio of theelement X or the elements X+X′ in the first antiferromagnetic layer 14at the interface adjacent to the pinned magnetic layer is greater thanin the second antiferromagnetic layer 15.

As described above, the composition ratio of the element X or theelements X+X′ in the second antiferromagnetic layer 15 is set to a valuenear 50 at % to enable transformation into an ordered lattice uponheat-treatment, requiring that the composition ratio of Mn is alsoaround 50 at %. In contrast, the composition ratio of the element X orthe elements X+X′ in the first antiferromagnetic layer 14 is set to avalue near 58 at % in order to reduce the influence of the restraintforce of pinned magnetic layer 3 at the interface adjacent to pinnedmagnetic layer 3, requiring a smaller Mn content to be present than inthe second antiferromagnetic layer 15.

Although the heat-treatment causes mutual diffusion of compositionsbetween the first antiferromagnetic layer 14 and the secondantiferromagnetic layer 15, the diffusion is still imperfect andantiferromagnetic layer 4 has such a gradient of composition ratio thatthe atomic percent of element X or elements X+X′ to that of Mn increasesprogressively towards pinned magnetic layer 3.

While it is not the Applicants' desire to be bound by a particulartheory, it is believed that a higher atomic percent of the element X orthe elements X+X′ is achieved in the region near the interface A than inthe region near the side B opposite to the interface A, as a result ofthe above-described diffusion.

The antiferromagnetic layer 4 is transformed from a disordered latticeinto an ordered lattice upon heat-treatment, so that at least part ofthe crystalline structure of the antiferromagnetic layer 4 has a CuAu—Itype face-centered cubic lattice (ordered lattice). In addition, it ispreferred that a non-aligned state is created at at least a part of theinterface adjacent to pinned magnetic layer 3.

When the aforementioned antiferromagnetic layer 4 is formed of a Pt—Mnalloy, the ratio c/a between lattice constants “a” and “c” ofantiferromagnetic layer 4 partly transformed into an ordered lattice,(i.e., antiferromagnetic layer 4 after heat-treatment), preferably fallwithin the range of 0.93 to 0.99.

A lattice constant ratio c/a below 0.93 allows almost the entirety ofthe crystalline structure of the antiferromagnetic layer to betransformed into an ordered lattice, producing undesirable effects suchas delamination due to a reduction in adhesion between theantiferromagnetic layer 4 and the pinned magnetic layer 3.

Conversely, a lattice constant ratio c/a above 0.99 allows almost theentirety of the crystalline structure of the antiferromagnetic layer toremain in the state of an ordered lattice, thereby reducing the exchangecoupling magnetic field at the interface between antiferromagnetic layer4 and pinned magnetic layer 3.

In accordance with the present invention, it is preferred that anon-aligned state is created at at least a part of the interface betweenpinned magnetic layer 3 and antiferromagnetic layer 4. Creation of sucha non-aligned state is facilitated by allowing pinned magnetic layer 3and antiferromagnetic layer 4 at at least a part of the above-mentionedinterface.

Thus, in accordance with the present invention, the structure afterheat-treatment may be such that a region exists in which the ratio ofthe atomic percent of element X or elements X+X′ to Mn increases towardspinned magnetic layer 3, and that at least a part of the crystallinestructure of antiferromagnetic layer 4 has a CuAu—I type face-centeredordered lattice, while antiferromagnetic layer 4 and pinned magneticlayer 3 have different lattice constants at at least a part of interfaceA. These features in combination also provide a greater exchangecoupling magnetic field than heretofore.

Alternatively, the structure after heat-treatment may be such that aregion exists in which the ratio of the atomic percent of the element Xor elements X+X′ to Mn increases towards pinned magnetic layer 3, andthat at least a part of the crystalline structure of antiferromagneticlayer 4 has a CuAu—I type face-centered ordered lattice, while theantiferromagnetic layer 4 and pinned magnetic layer 3 have differentcrystalline structures at at least a part of the interface A.

For instance, when the (111) plane of the pinned magnetic layer 3 hasbeen preferentially oriented in the direction of the film plane, the(111) plane of the antiferromagnetic layer 4 either has a smaller degreeof orientation than the (111) plane of the pinned magnetic layer 3, oris not oriented at all. Conversely, if the (111) plane of theantiferromagnetic layer 4 has been preferentially oriented in adirection parallel to the interface, the (111) plane of the pinnedmagnetic layer 3 either has a smaller degree of orientation than the(111) plane of the antiferromagnetic layer 4, or is not oriented at all.

Alternatively, the degrees of orientation of the (111) planes ofantiferromagnetic layer 4 and pinned magnetic layer 3 are either bothreduced with respect to the direction parallel to the interface betweenantiferromagnetic layer 4 and the pinned magnetic layer 3, or are notoriented at all.

It is also possible to facilitate creation of the non-aligned state atthe interface between pinned magnetic layer 3 and antiferromagneticlayer 4 and to obtain a greater exchange coupling magnetic field thanheretofore, by employing different crystal orientations for pinnedmagnetic layer 3 and the antiferromagnetic layer 4.

The elements constituting antiferromagnetic layer 4 after heat-treatmentdepend on the composition elements employed in the deposition of thefirst antiferromagnetic layer 14 and the second antiferromagnetic layer15 prior to heat-treatment. Therefore, when both the firstantiferromagnetic layer 14 and the second antiferromagnetic layer 15 aredeposited using the same elements, first antiferromagnetic layer 4 hasthe same elements over its entirety after heat-treatment.

It is preferred that first antiferromagnetic layer 14 is deposited withan antiferromagnetic material that affords a greater lattice constant,so that prior to heat-treatment, the non-aligned state at the interfaceis maintained. It is preferred that the second antiferromagnetic layer15 is deposited with an antiferromagnetic material that permits a smoothtransformation from a disordered lattice into an ordered lattice uponheat-treatment. Thus, antiferromagnetic materials having differentcomposition elements may be used for the first antiferromagnetic layer14 and the second antiferromagnetic layer 15.

For instance, when a Pt—Mn—Cr alloy is used as the material of the firstantiferromagnetic layer 14 and a Pt—Mn alloy is used as the material ofthe second antiferromagnetic layer 15, or when a Pt—Mn—Cr alloy is usedas the material of the first antiferromagnetic layer 14 and a Pd—Mnalloy is used as the material of the second antiferromagnetic layer 15,the kind of element X or elements X+X′ constituting the portion ofantiferromagnetic layer 4 near the interface A adjacent to pinnedmagnetic layer 3 may be partly the same as or different from that at theside B opposite to interface A.

As described above, the antiferromagnetic layer 4 after theheat-treatment has a region in which the ratio of atomic percent of theelement X or the elements X+X′ to Mn progressively increases towardspinned magnetic layer 3. It is, however, preferred that in the regionnear the interface A, the composition ratio of the element X or theelements X+X′ is not less than 50 at % and not greater than 65 at %,where the total composition ratio of all the elements constituting theantiferromagnetic layer is expressed as 100 at %. This range of thecomposition ratio of the element X or the elements X+X′ depends on thecomposition ratio of the element X or the elements X+X′ of the firstantiferromagnetic layer 14 as deposited (i.e., prior to theheat-treatment), and on the diffusion caused by heat-treatment.

More specifically, as described above, it is preferred that thecomposition ratio of the element X or the element X+X′ is not less than53 at % and not greater than 65 at %. It is considered that a diffusionof composition takes place also at the interface between the firstantiferromagnetic layer 14 and the pinned magnetic layer 3. For thesereasons, it is understood that the composition ratio of the element X orthe elements X+X′ in the region near the interface betweenantiferromagnetic layer 4 and pinned magnetic layer 3 is reduced fromthat obtained in the as-deposited state, thus allowing the compositionratio of the element X or the elements X+X′ to fall below 53 at %. Forthis reason, the preferred composition ratio of the element X or theelements X+X′ in the region near the interface A after heat-treatment isset to be at least 50 at % and not greater than 65 at %. A morepreferred composition ratio of the element X or the elements X+X′ is notless than 50 at % and not greater than 60 at %.

In accordance with the present invention, the composition ratio of theelement X or the elements X+X′ of the antiferromagnetic layer 4 near thesurface opposite to interface A is preferably not less than 44 at % andnot greater than 57 at %, where the total composition ratio of all theelements constituting the antiferromagnetic layer 4 is represented by100 at %. The composition ratio of the element X or the elements X+X′ inthe region near the side B depends on the composition ratio of theelement X or the elements X+X′ of the second antiferromagnetic layer 15in the as-deposited state (i.e., prior to the heat-treatment).

As stated above, it is preferred that the composition ratio of theelement X or the elements X+X′ of the second antiferromagnetic layer 15is preferably not less than 44 at % and not greater than 57 at %.Therefore, the preferred range of the element X or the elements X+X′ inthe region near the side B opposite to interface A in the state afterheat-treatment is set to be not less than 44 at % and not greater than57 at %, as is the case for the composition ratio in secondantiferromagnetic layer 15. A more preferred range of the element X orthe elements X+X′ is not less than 46 at % and not greater than 55 at %.

In accordance with the present invention, the region inantiferromagnetic layer 4 in which the composition ratio of the elementX or the elements X+X′ is not less than 46 at % and not greater than 53at % is not less than 70% and not more than 95% in terms of the volumeratio to total volume of antiferromagnetic layer 4. The fact that thevolume ratio of the above-mentioned region falls within theabove-specified range means that the transformation of antiferromagneticlayer 4 from the disordered lattice to an ordered lattice uponheat-treatment has been properly completed, thus providing a greaterexchange coupling magnetic field.

A description will now be given of a composition modulation occurring inthe direction of thickness of antiferromagnetic layer 4. As describedabove, in accordance with the present invention, the antiferromagneticlayer has a region in which the ratio of the atomic percent of theelement X or the element X+X′ to Mn increases towards pinned magneticlayer 3. In addition, antiferromagnetic layer 4 may have a compositionmodulation as described below.

An imaginary boundary plane extends parallel to the interface within thethickness of antiferromagnetic layer 4, so as to divideantiferromagnetic layer 4 in the thicknesswise direction into a firstregion between the imaginary boundary plane and interface A and a secondregion between the imaginary boundary plane and the side opposite tointerface A. In such a case, the above-mentioned ratio may linearly ornon-linearly increase from the second region to the first region acrossthe imaginary boundary plane.

For instance, the imaginary boundary mentioned above is represented by abroken line C. Thus, broken line C indicates the interface between firstantiferromagnetic layer 14 and second antiferromagnetic layer 15 of theantiferromagnetic layer 4 as deposited (i.e., prior to theheat-treatment, as in FIG. 2).

In the as-deposited state, the composition ratio of the element X or theelements X+X′ is greater in the first antiferromagnetic layer 14 than inthe second antiferromagnetic layer 15. It is understood thatheat-treatment causes diffusion of the composition across the interfacebetween first antiferromagnetic layer 14 and second antiferromagneticlayer 15. After heat-treatment, therefore, the above-mentioned ratio isgreater in the first region between interface A and the imaginaryboundary (broken line C) than in the second region between the imaginaryboundary (broken line C) and the side B opposite interface A. Inaddition, the above-mentioned ratio linearly or non-linearly increasesfrom the second region to the first region within a transient regionincluding the above-mentioned imaginary boundary. In particular, thenon-linear increase of the above-mentioned ratio tends to occur when thecomposition ratio of the element X or the elements X+X′ in the firstantiferromagnetic layer 14 is significantly greater than in the secondantiferromagnetic layer 15, in the as-deposited state.

In accordance with the present invention, the antiferromagnetic layer 4preferably has a region in which the composition ratio (atomic percent)of the element X or the elements X+X′ increases towards pinned magneticlayer 3. According to the present invention, in the antiferromagneticlayer as deposited (prior to heat-treatment), the composition ratio ofthe element X or the elements X+X′ in the first antiferromagnetic layer14 adjacent to pinned magnetic layer 3 is determined to be greater thanin the second antiferromagnetic layer 15. It is therefore consideredthat, despite any composition modulation caused by heat-treatment in theregion between first antiferromagnetic layer 14 and secondantiferromagnetic layer 15, the composition ratio (atomic percent) ofthe element X or the elements X+X′ in the portion adjacent to pinnedmagnetic layer that was constituted by the first antiferromagnetic layerbefore heat-treatment is still greater than in the region that wasconstituted by the second antiferromagnetic layer, whereby theabove-mentioned composition modulation takes place at a certain portion.

In accordance with the present invention, it is preferred that a regionexists near the interface A between antiferromagnetic layer 4 and pinnedmagnetic layer 3, in which the atomic percent of the element X or theelements X+X′ decreases towards pinned magnetic layer 3.

While it is not the Applicants' desire to be bound by a particulartheory, it is believed that a diffusion of composition takes placebetween antiferromagnetic layer 4 and pinned magnetic layer 3 in theregion of antiferromagnetic layer 4 near interface A. Such a diffusionwill result in a smaller composition ratio of the element X or theelements X+X′ in the region near interface A than was achieved in theas-deposited state.

When antiferromagnetic layer 4 has a region in which the compositionratio of element X or element X+X′ decreases towards pinned magneticlayer 3 in the region near interface A, as in the present invention, thetransformation from a disordered lattice into an ordered lattice isproperly effected by antiferromagnetic layer 4 in the region nearinterface A, whereby a large exchange coupling magnetic field isgenerated.

In the heat-treated antiferromagnetic layer 4, it is preferred that thecomposition ratio of element X or elements X+X′ is maximized in theregion which immediately underlies interface A adjacent to pinnedmagnetic layer 3. It is preferred this region has a thickness of notsmaller than 3 Å and not greater than 30 Å, as measured from theinterface A in the thicknesswise direction towards side B oppositeinterface A. This is the preferred range of thickness of firstantiferromagnetic layer 14 in the as-deposited state prior toheat-treatment.

In accordance with the present invention, a protective layer 7 made of,for example, Ta or the like is formed on the side B of theantiferromagnetic layer 4 opposite to the interface A adjacent to pinnedmagnetic layer 3. It is considered that a composition modulation due toheat-treatment occurs also at the boundary between secondantiferromagnetic layer 15 as deposited and protective layer 7.

Thus, in accordance with the present invention, a region may exist inthe antiferromagnetic layer 4 near the side opposite pinned magneticlayer 3, in which the composition ratio of the element X or the elementsX+X′ decreases towards the above-mentioned side of antiferromagneticlayer 4.

In accordance with the present invention, the antiferromagnetic layer 4preferably has a thickness not smaller than 73 Å. As explained abovewith reference to FIG. 2, the thickness of the first antiferromagneticlayer 14 should be at least 3 Å, while the thickness of secondantiferromagnetic layer 15 should be at least 70 Å, so that the totalthickness of antiferromagnetic layer 4 should be at least 73 Å.

Thus, in accordance with the present invention, the minimum thicknessrequired for antiferromagnetic layer 4 is 73 Å, which is significantlysmaller than that required in conventional structures. This means thatthe gap width can be reduced when the laminate structure of FIG. 3 isused as a thin-film magnetic head.

Although in the embodiment described above, the antiferromagnetic layer4 as deposited (prior to heat-treatment) is composed of a dual-layerstructure having first antiferromagnetic layer 14 and secondantiferromagnetic layer 15, this is only illustrative and otherproduction methods can be employed.

For instance, an exchange coupling magnetic field greater than those ofconventional structures can be obtained even when antiferromagneticlayer 4 as deposited (prior to heat-treatment) is composed of a singlelayer, provided the production process described below is employed.

More specifically, in accordance with the present invention,antiferromagnetic layer 4 may be formed by a sputtering process in whichan element X and Mn are used as sputtering targets, where the element Xis one or more elements selected from the group consisting of Pt, Pd,Ir, Rh, Ru, and Os, while the sputtering gas pressure is progressivelyincreased in the direction away from pinned magnetic layer 3 duringdeposition of antiferromagnetic layer 4, As a result, the compositionratio (atomic percent) of element X is reduced in the direction awayfrom the side of antiferromagnetic layer 4 adjacent to pinned magneticlayer 3. When this method is used, it is preferred that a non-alignedstate is obtained at at least a part of the interface betweenantiferromagnetic layer 4 and pinned magnetic layer 3.

Representing the composition ratio of all elements constituting theportion of antiferromagnetic layer 4 near the side opposite theinterface, it is preferred that the composition ratio of element X isnot less than 44 at % and not greater than 57 at %, more preferably notless than 46 at % and not more than 55 at %.

By virtue of these features, the portion of antiferromagnetic layer 4near the interface between antiferromagnetic layer 4 and pinned magneticlayer 3 is freed from the influence of the restraint force produced bythe crystalline structure of pinned magnetic layer 3. The remainingportion of antiferromagnetic layer 4 other than the region near theinterface can have a composition ratio (at %) of element X whichapproaches an ideal composition for facilitating transformation from adisordered lattice into an ordered lattice upon heat-treatment.

It is therefore possible to effect a proper transformation ofantiferromagnetic layer 4 as deposited from a disordered lattice into anordered lattice by effecting a heat-treatment on the antiferromagneticlayer as deposited. Further, since the heat-treatment possibly causesdiffusion of elements in antiferromagnetic layer 4, the transformationfrom a disordered lattice into an ordered lattice properly takes placein antiferromagnetic layer 4, thus providing a greater exchange couplingmagnetic field than in conventional structures.

When a non-aligned state exists at the above-mentioned interface, theantiferromagnetic layer 4 is conveniently freed from the restraint forceproduced by the crystalline structure of pinned magnetic layer 3, sothat the transformation of the whole antiferromagnetic layer 4 ispromoted.

It is also preferred that antiferromagnetic layer 4 has a thickness notsmaller than 73 Å. As explained above with reference to FIG. 2, thisminimum value of 73 Å is the sum of the minimum thicknesses required forthe combination of first antiferromagnetic layer 14 and secondantiferromagnetic layer 15, which together form antiferromagnetic layer4.

Referring again to FIG. 2, the minimum required thickness of firstantiferromagnetic layer is 3 Å, while the minimum required thickness forsecond antiferromagnetic layer 15 is 70 Å, so that the minimum thicknessrequired for the antiferromagnetic layer is set to be 73 Å.

The composition ratio of element X is preferably not smaller than 53 at% and not greater than 65 at %, more preferably not less than 55 at %and not greater than 60 at %, in the thicknesswise region of at least 3Å as measured from the interface adjacent to pinned magnetic layer 3,even when antiferromagnetic layer 4 as deposited (prior toheat-treatment) is formed of a single layer. The composition ratio ofall the elements in this region is expressed as 100 at %. The remainingregion has a thickness of 70 Å or greater preferably has a compositionratio of element X not smaller than 44 at % and not greater than 57 at%, more preferably not less than 46 at % and not greater than 55 at %.With these features, it is possible to obtain an exchange couplingmagnetic field of 7.9

10⁴ A/m or greater, as in the case of the structure shown in FIG. 2.

In accordance with the present invention, antiferromagnetic layer 4 mayalso be formed by a sputtering process in which an element X, an elementX′ and Mn are used as sputtering targets, where the element X′ is one ormore elements selected from the group consisting of Ne, Ar, Kr, Xe, Be,B, C, N, Mg, Al, Si, P, Ti, V, Cr, Fe, Co, Ni, Cu, Zn, Ga, Ge, Zr, Nb,Mo, Ag, Cd, Sn, Hf, Ta, W, Re, Au, Pb and a rare earth element, whilethe sputtering gas pressure is progressively increased in the directionaway from pinned magnetic layer 3 during deposition of antiferromagneticlayer 4. As a result, the composition ratio (atomic percent) of theelements X+X′ is reduced in the direction away from the side ofantiferromagnetic layer 4 adjacent to pinned magnetic layer 3.

Preferably, the element X′ invades the interstices of a space latticeformed by element X and Mn, or which substitutes for a portion of thelattice points of the crystalline structure formed of element X and Mn.Such an element X′ allows the lattice constant of the X—Mn—X′ alloy tobe expanded over the lattice constant of the X—Mn alloy, thus making iteasy to maintain a non-aligned state at the interface adjacent to pinnedmagnetic layer 3.

As stated above, according to the present invention, it is preferredthat an unaligned state is created at at least a part of the interfacebetween antiferromagnetic layer 4 and pinned magnetic layer 3. One ofthe methods for creating such a non-aligned state is to employ, at atleast a part of the interface, different lattice constants forantiferromagnetic layer 4 and pinned magnetic layer 3.

Thus, the present invention may be carried out such that when theantiferromagnetic layer 4 is formed by a sputtering process using anelement X and Mn as sputtering targets or using elements X+X′ and Mn assputtering targets, the sputtering gas pressure is progressivelyincreased in the direction away from pinned magnetic layer 3 duringdeposition of antiferromagnetic layer 4. As a result, the compositionratio (atomic percent) of the element X or the elements X+X′ is reducedin the direction away from the side of antiferromagnetic layer 4adjacent to pinned magnetic layer 3. During deposition ofantiferromagnetic layer 4, different lattice constants are employed forantiferromagnetic layer 4 and pinned magnetic layer 3 at at least a partof the interface therebetween.

Alternatively, the invention may be carried out such that when theantiferromagnetic layer 4 is formed by a sputtering process using anelement X and Mn as sputtering targets or using elements X+X′ and Mn assputtering targets, the sputtering gas pressure is progressivelyincreased in the direction away from pinned magnetic layer 3 duringdeposition of antiferromagnetic layer 4. As a result, the compositionratio (atomic percent) of the element X or the elements X+X′ is reducedin the direction away from the side of antiferromagnetic layer 4adjacent to pinned magnetic layer 3. During deposition ofantiferromagnetic layer 4, different crystal orientations are employedfor antiferromagnetic layer 4 and pinned magnetic layer 3 at at least apart of the interface between antiferromagnetic layer 4 and pinnedmagnetic layer 3. Creation of a non-aligned state at at least a part ofthe interface between antiferromagnetic layer 4 and pinned magneticlayer 3 is also facilitated by causing antiferromagnetic layer 4 andpinned magnetic layer 3 to have different crystal orientations.

By effecting a heat-treatment of the laminate structure formed by thedescribed process, it is possible to obtain a laminate structure similarto that shown in FIG. 3.

Thus, the antiferromagnetic layer 4 after deposition is formed of anantiferromagnetic material containing an element X and Mn or,alternatively, elements X+X′ and Mn, and has a region in which the ratioof the atomic percent of the element X or the elements X+X′ increasestowards the antiferromagnetic layer 3. The crystalline structure of atleast a part of the antiferromagnetic layer has a CuAu—I typeface-centered cubic ordered lattice, and a non-aligned state is createdat at least part of the interface A.

FIG. 4 shows a laminate structure employing a seed layer 22 in anas-deposited state (i.e., in a state prior to a heat-treatment). FIG. 5shows the laminate structure obtained by effecting heat-treatment of thelaminate structure shown in FIG. 4.

The laminate structure of FIG. 4 and, hence, the laminate structure ofFIG. 5, are used in the production of a single-spin valve typemagnetoresistive sensor having an antiferromagnetic layer 4 underlying apinned magnetic layer 3. An example is shown in FIG. 6.

As the first step, a seed layer 22 is formed on an underlying layer 6,and then an antiferromagnetic layer 4 is formed on the seed layer 22.

The underlying layer 6 is preferably formed of at least one elementselected from the group consisting of Ta, Hf, Nb, Zr, Ti, Mo, and W. Theunderlying layer 6 is intended to preferentially align the (111) planeof seed layer 22 in the direction parallel to the interface betweenunderlying layer 6 and seed layer 22. The underlying layer has athickness of, for example, 50 Å.

The seed layer 22 is mainly constituted by face-centered cubic crystals,with the (111) plane preferentially oriented in the direction parallelto the interface between the seed layer 22 and the antiferromagneticlayer 4. It is preferred that the seed layer is formed of a Ni—Fe alloyor a Ni—Fe—Y alloy, where Y is at least one element selected from thegroup consisting of Cr, Rh, Ta, Hf, Nb, Zr, and Ti. The seed layer 22formed from such a material on underlying layer 6 serves to facilitatethe preferential orientation of the (111) plane in the directionparallel to the interface adjacent antiferromagnetic layer 4.

Preferably, the seed layer 22 is formed of a non-magnetic material. Thenon-magnetic nature of the seed layer 22 serves to enhance the specificresistance of the seed layer 22. Shunting of the sense current into seedlayer 22 causes an undesirable reduction in the ratio of resistancevariation (ΔMR), or the generation of Barkhausen noise.

When a non-magnetic material is used as the material of the seed layer22, the Ni—Fe—Y alloy, Y being at least one element selected from thegroup consisting of Cr, Rh, Ta, Hf, Nb, Zr, and Ti, may be selected tobe a non-magnetic material, from the materials mentioned above. Such amaterial has a face-centered crystalline structure. Moreover, the (111)plane of this material can easily be aligned in the directionpreferentially parallel to the interface adjacent antiferromagneticlayer 4. The seed layer 22 has a thickness of, for example, about 30 Å.

As will be seen from FIG. 4, the antiferromagnetic layer 4 formed onseed layer 22 is composed of a laminate structure having a firstantiferromagnetic layer 23, a second antiferromagnetic layer 24, and athird antiferromagnetic layer 25.

In accordance with the present invention, each of the firstantiferromagnetic layer 23, second antiferromagnetic layer 24, and thirdantiferromagnetic layer 25 may be formed from an antiferromagneticmaterial which contains an element X and Mn, wherein X is one or moreelements selected from the group consisting of Pt, Pd, Ir, Rh, Ru, andOs.

Alternatively, each of the first antiferromagnetic layer 23, secondantiferromagnetic layer 24, and third antiferromagnetic layer 25 may beformed from an antiferromagnetic material which contains an element X,an element X′ and Mn, wherein the element X′ is one or more elementsselected from the group consisting of Ne, Ar, Kr, Xe, Be, B, C, N, Mg,Al, Si, P, Ti, V, Cr, Fe, Co, Ni, Cu, Zn, Ga, Ge, Zr, Nb, Mo, Ag, Cd,Sn, Hf, Ta, W, Re, Au, Pb and a rare earth element.

In each of the above-described structures, the X—Mn—X′ alloy ispreferably either an interstitial solid solution in which the element X′has entered the interstices of a space lattice formed by the element Xand Mn, or a substitutional solid solution in which a portion of thelattice points of the crystal lattice formed by the element X and Mn hasbeen substituted by the element X′. Å The X—Mn—X′ alloy in the form ofan interstitial solid solution or a substitutional solid solution has anexpanded lattice constant compared to the X—Mn alloy.

In accordance with the present invention, the composition ratio of theelement X or the elements X+X′ in each of the first and thirdantiferromagnetic layers 23 and 25 is determined to be greater than thatin the second antiferromagnetic layer 24.

The second antiferromagnetic layer 24 formed between the first and thirdantiferromagnetic layers 23 and 25 is made of an antiferromagneticmaterial which approximates an ideal composition for the transformationfrom a disordered lattice to an ordered lattice by heat-treatment.

The reason why the composition ratio of the element X or the elementsX+X′ in each of the first and third antiferromagnetic layers 23 and 25is determined to be greater than that in the second antiferromagneticlayer 24 is the same as that described above with reference to FIG. 2.Namely, it is intended that restraint forces produced by the crystallinestructures of the pinned magnetic layer 3 and the seed layer 22 that actat the respective interfaces are diminished, so as to allow an easytransformation of the antiferromagnetic layer 4 upon heat-treatment.

Preferably, the composition ratio of the element X or elements X+X′ ofeach of the first antiferromagnetic layer 23 and the thirdantiferromagnetic layer 25 is not less than 53 at % and not greater than65 at %, more preferably not less than 55 at % and not greater than 60at %. Preferably, the thickness of each of the first antiferromagneticlayer 23 and the third antiferromagnetic layer 25 is not less than 3 Åand not greater than 30 Å. For instance, in the embodiment shown in FIG.4, the thickness of each of the first antiferromagnetic layer 23 and thethird antiferromagnetic layer 25 is about 10 Å.

Preferably, the composition ratio of the element X or elements X+X′ ofthe second antiferromagnetic layer 24 is not less than 44 at % and notgreater than 57 at %, more preferably not less than 46 at % and notgreater than 55 at %. A composition ratio of the element X or theelements X+X′ falling within this range permits easy transformation ofthe second antiferromagnetic layer 24 from a disordered lattice into anordered lattice by heat-treatment. Preferably, the thickness of thesecond antiferromagnetic layer 24 is not less than 70 Å. For instance,in the embodiment shown in FIG. 4, the thickness of the secondantiferromagnetic layer 24 is about 100 Å.

Preferably, each of the first, second and third antiferromagnetic layers23, 24 and 25 is formed by sputtering. It is also preferred that thesputtering used for each of the first antiferromagnetic layer 23 and thethird antiferromagnetic layer 25 is conducted at a lower sputter gaspressure than for the second antiferromagnetic layer 24. Such a lowersputtering gas pressure provides a greater composition ratio of theelement X or the elements X+X′ for each of the first and thirdantiferromagnetic layers 23 and 25 than for the second antiferromagneticlayer 24.

Alternatively, in accordance with the present invention, theantiferromagnetic layer 4, as deposited, is not formed of athree-layered laminate structure as described but of a single-layeredstructure in accordance with the process described below. Even when sucha process is used, it is possible to create a suitable variation of thecomposition ratio (atomic percent) of the element X or the elements X+X′in the direction of thickness of the antiferromagnetic layer 4.

The antiferromagnetic layer 4 is deposited by using the element X and Mnor, alternatively, the elements X+X′ and Mn, as sputtering targets,while the sputtering gas pressure is progressively increased in thedirection away from seed layer 22. When the deposition has proceeded toabout a half of the final thickness, the sputtering gas pressure isprogressively decreased until the deposition of the antiferromagneticlayer is completed.

When such a deposition technique is used, the composition ratio (atomicpercent) of the element X or the elements X+X′ is progressivelyincreased from the interface adjacent to seed layer 22 towards thethicknesswise central region of antiferromagnetic layer 4, and thenprogressively decreased towards the interface adjacent to pinnedmagnetic layer 3.

It is thus possible to form an antiferromagnetic layer 4 in which thecomposition ratio (atomic percent) of the element X or the elements X+X′is large at the interface adjacent to seed layer 22 and at the interfaceadjacent to pinned magnetic layer 3, and is small at the thicknesswisecentral region of antiferromagnetic layer 4.

Preferably, the composition ratio of the element X or the compositionratio of the elements X+X′ of the antiferromagnetic layer to the totalcomposition ratio (100 at %) of all the elements constituting theantiferromagnetic layer 4 is not less than 53 at %and not more than 65at %, preferably not less than 55 at % and not more than 60 at %, in theregion near the interface between antiferromagnetic layer 4 and thepinned magnetic layer, as well as in the region near antiferromagneticlayer 4 and seed layer 22.

In these methods of the present invention, it is also preferred that thecomposition ratio of the element X or the composition ratio of theelements X+X′ of antiferromagnetic layer 4 is not less than 44 at %andnot more than 57 at %, preferably not less than 46 at %and not more than55 at %, in the thicknesswise central region of the antiferromagneticlayer 4 and the ferromagnetic layer. It is also preferred that thethickness of the antiferromagnetic layer is 76 Å or greater.

The pinned magnetic layer 3 is formed on antiferromagnetic layer 4, asshown in FIG. 4. In the embodiment shown in FIG. 4, the pinned magneticlayer 3 has a so-called ferromagnetic state constituted by three layers,as in the embodiment shown in FIG. 2, a Co film 11, a Ru film 12, and aCo film 13. The Co film 11 is formed to have a thickness of about 20 Å,the Ru film 12 is formed to have a thickness of about 8 Å, and the Cofilm 13 is formed to have a thickness of about 15 Å.

As a result of heat-treatment, the crystalline structure ofantiferromagnetic layer 4 is properly transformed to change from adisordered lattice to an ordered lattice, without being restrained bythe restraint forces produced by seed layer 22 and pinned magnetic layer3 at the interfaces adjacent to seed layer 22 and pinned magnetic layer3. As a result, an exchange coupling magnetic field is generated at theinterface between antiferromagnetic layer 4 and pinned magnetic layer 3,and the magnetization of pinned magnetic layer 3 is formed into a singlemagnetic domain in the vertical direction Y.

In accordance with the present invention, a non-aligned state is createdat at least a part of the interface between seed layer 22 and pinnedmagnetic layer 3. The presence of such a non-aligned state reduces theinfluence of the restraint forces produced by seed layer 22 and pinnedmagnetic layer 3 at the respective interfaces, thus promotingtransformation of the antiferromagnetic layer 4 into an orderedstructure.

In accordance with the present invention, the antiferromagnetic layer 4has first and third antiferromagnetic layers 23 and 25 which are formedat the sides contacting seed layer 22 and pinned magnetic layer 3, eachof which has a large composition ratio of the element X or the elementsX+X′. A second antiferromagnetic layer 24 interposed between firstantiferromagnetic layer 23 and third antiferromagnetic layer 25 has acomposition which is easy to transform from a disordered lattice to anordered lattice. Therefore, transformation proceeds at the secondantiferromagnetic layer 24 as a result of heat-treatment, whilediffusion of composition takes place at the boundaries between firstantiferromagnetic layer 23 and second antiferromagnetic layer 24, andbetween second antiferromagnetic layer 24 and third antiferromagneticlayer 25. As a result, transformation from the disordered lattice intothe ordered lattice takes place in the first antiferromagnetic layer 23and in the third antiferromagnetic layer 25, while a nonaligned state isproperly maintained at the interface between first antiferromagneticlayer 23 and seed layer 22, as well as at the interface between thirdantiferromagnetic layer 25 and pinned magnetic layer 3. Thus, a propertransformation occurs in the whole antiferromagnetic layer 4. Inaccordance with the present invention, it is possible to expect a propertransformation and, hence, a greater exchange coupling magnetic field,specifically an exchange magnetic coupling of 7.9×10⁴ A/m or greater.

A non-magnetic intermediate layer 2 formed, for example, from Cu isformed on pinned magnetic layer 3, and a free magnetic layer 1 is formedon the non-magnetic intermediate layer 2.

The free magnetic layer 1 is formed of, for example, a Ni—Fe alloy film9 and a Co film 10. The non-magnetic intermediate layer 2 has athickness of, for example, 22 Å, while the N—Fe alloy film 9 has athickness of about 45 Å. The Co film 10 has a thickness of about 5 Å.

Then, a protective layer 7 formed, for example, ofTa is formed on freemagnetic layer 1, as shown in FIG. 4. The protective layer 7 has athickness of, for example, about 30 Å.

In accordance with the present invention, as stated above, seed layer 22is formed on the lower side of antiferromagnetic layer 4, i.e., on theside of antiferromagnetic layer 4 opposite to the interface adjacentpinned magnetic layer 3. The seed layer is constituted primarily of aface-centered crystalline structure, with the (111) plane oriented in adirection parallel to the interface adjacent antiferromagnetic layer 4.

Therefore, the crystals of the layers on seed layer 22, starting fromantiferromagnetic layer 4 and terminating in free magnetic layer 1, arealso liable to be aligned such that their (111) planes arepreferentially oriented in a direction parallel to the above-mentionedinterface, thereby allowing growth of large crystal grains. Such largecrystal grains increase the ratio of resistance variation (ΔMR),offering improved reproduction characteristics.

As described above, the embodiment shown in FIG. 4 provides not onlyimproved ratio of resistance variation but also a large exchangecoupling magnetic field. The ratio of resistance variation is reducedwhen the exchange coupling magnetic field is reduced. To a certainextent, exchange coupling magnetic field is also necessary from theviewpoint of improving in the ratio of resistance variation.

A heat-treatment is conducted after deposition of the layers, fromunderlying layer 6 up to protective layer 7, as shown in FIG. 4. Theseed layer 22 formed on underlying layer 6 formed of Ta or the likestill retains its crystalline structure primarily constituted byface-centered cubic crystals with the (111) plane oriented in adirection parallel to the interface adjacent antiferromagnetic layer 4.

The antiferromagnetic layer 4 formed on seed layer 22 has a crystallinestructure at least part of which is formed of a CuAu—I typeface-centered ordered lattice. Each of the layers from antiferromagneticlayer 4 to free magnetic layer 1 has its (111) planes preferentiallyoriented in the direction parallel to the interface. Further, anon-aligned state is created at at least a part of the interface Ibetween antiferromagnetic layer 4 and the seed layer, and at at least apart of the interface H between antiferromagnetic layer 4 and pinnedmagnetic layer 3.

As described above, in the present invention, layers fromantiferromagnetic layer 4 to free magnetic layer 1 have crystallinestructures with their (111) planes oriented in the direction parallel tothe interface and, at the same time, have large crystal grains, thusoffering a greater resistance variation ratio (ΔMR).

As described above, seed layer 22 is preferably formed from a Ni—Fealloy or a Ni—Fe—Y alloy, where Y is at least one element selected fromthe group consisting of Cr, Rh, Ta, Hf, Nb, Zr, and Ti, in particularfrom a non-magnetic alloy. The non-magnetic nature of seed layer 22serves to enhance the specific resistance of the seed layer 22, so thatshunting of a sense current from the conductive layer to seed layer 22is suppressed, thereby affording a greater resistance variation ratio,while suppressing generation of Barkhausen noise.

Furthermore, in accordance with the present invention, a non-alignedstate is created at at least a part of the interface I betweenantiferromagnetic layer 4 and seed layer 22, and at at least a part ofthe interface h between antiferromagnetic layer 4 and pinned magneticlayer 3. Moreover, the crystalline structure of at least a part ofantiferromagnetic layer 4 has been transformed into a CuAu—I typeface-centered cubic ordered lattice structure, suggesting thatantiferromagnetic layer 4 has been properly transformed from adisordered lattice structure into an ordered lattice structure. Thus, agreater exchange coupling magnetic field between antiferromagnetic layer4 and pinned magnetic layer 3 than heretofore possible, specifically anexchange coupling magnetic field of 7.9×10⁴ A/m or greater, is obtained.

In accordance with the present invention, antiferromagnetic layer 4 andseed layer 22 may have different lattice constants at at least a part ofinterface I, and antiferromagnetic layer 4 and pinned magnetic layer 3may have different lattice constants at at least a part of interface H.This permits a non-aligned state to be created at at least a part ofinterface I between antiferromagnetic layer 4 and seed layer 22 and atat least a part of interface H between antiferromagnetic layer 4 andpinned magnetic layer 3.

The heat-treatment causes a diffusion of composition at the interface Fbetween first antiferromagnetic layer 23 and second antiferromagneticlayer 24, and at the interface G between third antiferromagnetic layer25 and second antiferromagnetic layer 24, so that the interfaces F and Gbecome obscure and indefinite after heat-treatment.

The antiferromagnetic layer 4 is preferably formed from anantiferromagnetic material containing an element X and Mn, where theelement X is one or more elements selected from the group consisting ofPt, Pd, Ir, Rh, Ru, and Os, or from an antiferromagnetic elementcontaining an element X, an element X′ and Mn, where the element X′ isone or more elements selected from the group consisting of Ne, Ar, Kr,Xe, Be, B, C, N, Mg, Al, Si, P, Ti, V, Cr, Fe, Co, Ni, Cu, Zn, Ga, Ge,Zr, Nb, Mo, Ag, Cd, Sn, Hf, Ta, W, Re, Au, Pb and a rare earth element.The aforementioned X—Mn—X′ alloy, when used as the material of theantiferromagnetic layer 4, preferably has the form of either aninterstitial solid solution in which the element X′ has enteredinterstices of the space lattice constituted by element X and Mn, or asubstitutional solid solution in which the element X′ has substitutedfor a portion of the lattice points of the crystal lattice formed of theelement X and Mn. The X—Mn—X′ alloy can expand the lattice constant overthat of the X—Mn alloy, making it possible to properly maintain thenon-aligned state at the interface between seed layer 22 and pinnedmagnetic layer 3.

Preferably, the antiferromagnetic layer 4 after heat-treatment has aregion in which the ratio of the atomic percent of element X or elementsX+X′ increases towards seed layer 22.

The presence of such a composition modulation means that thetransformation into the ordered lattice structure has been properlyeffected by heat-treatment. The region of the above-mentionedcomposition modulation can be achieved by determining the compositionratio of the element X or the elements X+X′ in the thirdantiferromagnetic layer 25 to be greater than that in the secondantiferromagnetic layer 24 in the as-deposited state (i.e., in the stateshown in FIG. 4 prior to the heat-treatment), or by varying the sputtergas pressure during deposition of antiferromagnetic layer 4 such thatthe atomic percent of the element X or the elements X+X′ isprogressively decreased towards the thicknesswise center ofantiferromagnetic layer 4. With this feature, it is considered that thetransformation into the ordered lattice structure is properly performedat the interface I between seed layer 22 and antiferromagnetic layer 4,without being influenced by any restraint force produced by thecrystalline structure of seed layer 22. Thus, a greater exchangecoupling magnetic field than heretofore is obtained.

In addition to the above-described composition modulation, theantiferromagnetic layer 4 has a region in which the ratio of the atomicpercent of element X or elements X+X′ increases towards pinned magneticlayer 3. This can be achieved by determining the composition ratio ofthe element X or the elements X+X′ in the first antiferromagnetic layer23 to be greater than that in the second antiferromagnetic layer 24 inthe as-deposited state (i.e., in the state shown in FIG. 4 prior toheat-treatment), or by varying the sputter gas pressure duringdeposition of antiferromagnetic layer 4 such that the composition ratio(atomic percent) of the element X or the elements X+X′ is progressivelydecreased from the thicknesswise central region towards pinned magneticlayer 3.

Thus, the antiferromagnetic layer 4 adjoining seed layer 22 shown inFIG. 5 has a thicknesswise region between the thicknesswise centralregion and the pinned magnetic layer 3 in which the atomic percent ofthe element X or the elements X+X′ to Mn progressively increases towardspinned magnetic layer 3, and a thicknesswise region between thethicknesswise central region and seed layer 22 in which the atomicpercent of the element X or the elements X+X′ to Mn progressivelyincreases towards seed layer 22.

Representing by 100 at % the composition ratio of all elementsconstituting the region of first antiferromagnetic layer 2 near theinterface I, as well as the region of first antiferromagnetic layer nearthe interface H, the composition ratio of the element X or the elementsX+X′ is preferably not less than 50 at % and not greater than 65 at %.This range is derived from the proper composition range (from 53 at % to65 at %) of the first antiferromagnetic layer 23 and the thirdantiferromagnetic layer 25 in the as-deposited state prior toheat-treatment. Due to heat-treatment induced diffusions of compositionsat the interface I between the antiferromagnetic layer 4 and the seedlayer 22 and at the interface H between the antiferromagnetic layer 4and the pinned magnetic layer 3, the minimum value (50 at %) of thecomposition ratio allowed in the antiferromagnetic layer 4 afterheat-treatment is smaller than the above-mentioned minimum value (53 at%) allowed for the first antiferromagnetic layer 23 and the thirdantiferromagnetic layer 25. The composition ratio of the element X orthe elements X+X′ is preferably not less than 50 at % and not greaterthan 60 at % in each of the interface I adjacent seed layer 22 and theinterface H adjacent pinned magnetic layer 3.

The composition ratio (atomic percent) of the element X or the elementsX+X′ after heat-treatment is preferably not less than 44 at % and notgreater than 57 at % in the thicknesswise central region. This range ofthe composition ratio is derived from the preferred composition ratio(from 44 at % to 57 at %) of the element X or the elements X+X′ of thesecond antiferromagnetic layer 24 in the as-deposited state (i.e., priorto heat-treatment). More preferably, the above-mentioned compositionratio of the element X or the elements X+X′ is not less than 46 at % andnot greater than 55 at %.

Two imaginary boundary planes extend parallel to the interfaces adjacentto pinned magnetic layer 3 and the seed layer 22, within the thicknessof antiferromagnetic layer 4. The ratio of the atomic percent of theelement X or the elements X+X′ to Mn is greater in a third region and ina first region than in a second region, wherein the third region is aregion between the interface H adjacent to pinned magnetic layer 3 and asecond imaginary boundary plane adjacent to interface H, the firstregion is a region between interface I adjacent to seed layer 22 and afirst imaginary boundary plane adjacent to interface I, and the secondregion is the region between the two imaginary boundary planes, with theabove-mentioned ratio preferably increasing linearly or non-linearlyfrom the second region towards the first region across the firstimaginary boundary plane, and from the second region towards the thirdregion across the second imaginary boundary regions.

For instance, it is assumed here that a broken line G as shown in FIG. 5indicates the first imaginary boundary plane, while a broken line Fshown in FIG. 5 indicates the second imaginary boundary plane. Thebroken lines F and G are drawn at thicknesswise positions where theinterface between first antiferromagnetic layer 23 and secondantiferromagnetic layer 24 and the interface between the secondantiferromagnetic layer 24 and third antiferromagnetic layer 25 existedin the as-deposited state prior to heat-treatment.

In the as-deposited structure prior to heat-treatment, the compositionratio of the element X or the elements X+X′ is greater in the first andthird antiferromagnetic layers 23 and 25 than in the secondantiferromagnetic layer 24. It is understood that a subsequentheat-treatment causes diffusions at the interfaces between secondantiferromagnetic layer 24 and first and third antiferromagnetic layers23, 25, so that in the state after heat-treatment, the ratio of theatomic percent of the element X or the elements X+X′ to Mn in the thirdregion between interface H facing pinned magnetic layer 3 and the secondimaginary boundary plane (broken line F) adjacent interface H, as wellas in the first region between the interface I facing the seed layer 22and the first imaginary boundary pane (broken line G) adjacent interfaceI, is greater than the ratio of the atomic percent of the element X orthe elements X+X′ to Mn in the second region between these imaginaryboundary planes. In addition, the ratio of atomic percent of the elementX or the elements X+X′ to Mn linearly or non-linearly increases from thesecond region towards the third region across the second imaginaryboundary plane (broken line F) and, likewise, increases linearly ornon-linearly from the second region towards the first region across thefirst imaginary boundary plane (broken line G). In particular, it isalso considered that the non-linear change described above is liable tooccur when the composition ratio of the element X or the elements X+X′is significantly greater in each of the first and thirdantiferromagnetic layers 23 and 25 than in the second antiferromagneticlayer 24.

It is thus understood that, in the antiferromagnetic layer 4 afterheat-treatment, due to the fact that the composition ratio of theelement X or the elements X+X′ is greater in each of the first and thirdantiferromagnetic layers 23 and 25 than in the second antiferromagneticlayer 24, the composition ratio (atomic percent) of the element X or theelements X+X′ increases from a certain thicknesswise central portiontowards the interface H adjacent to pinned magnetic layer 3 andincreases also from the above-mentioned thicknesswise central portiontowards the interface I adjacent to seed layer 22.antiferromagnetic

While it is not the Applicants' desire to be bound to a particulartheory, it is believed that heat-treatment causes diffusions of thecompositions between antiferromagnetic layer 4 and pinned magnetic layer3 across interface H, and between antiferromagnetic layer 4 and seedlayer 22 across interface I. As a result, the composition ratio of theelement X or the elements X+X′ is decreased from that achieved in theas-deposited state, at each of the regions near interfaces H and I.

In accordance with the present invention, therefore, antiferromagneticlayer 4 preferably has a region near interface I adjacent to seed layer22, in which the atomic percent of the element X or the elements X+X′decreases towards seed layer 22, as well as a region near interface Hadjacent to pinned magnetic layer 3, in which the atomic percent of theelement X or the elements X+X′ decreases towards pinned magnetic layer3.

The diffusion of compositions occurring at each of the interface Hbetween antiferromagnetic layer 4 and pinned magnetic layer 3 andinterface I between antiferromagnetic layer 4 and seed layer 22 causesthe atomic percent of the element X or the elements X+X′ to be decreasedin the region near each of these interfaces H and I from the atomicpercent that was achieved in the as-deposited state. As a result, aproper transformation from disordered lattice into an ordered latticetakes place in the regions near interfaces H and I, making it possibleto produce a large exchange coupling magnetic field.

Preferably, in the heat-treated antiferromagnetic layer 4, the region inwhich the composition ratio (atomic percent) of the element X or theelements X+X′ decreases towards interface H is a region which has athickness not less than 3 Å and not greater than 30 Å, as measured fromthe interface H towards the thicknesswise center of theantiferromagnetic layer 4. The region in which the composition ratio(atomic percent) of the element X or the elements X+X′ decreases towardsinterface I is a region which has a thickness not less than 3 Å and notgreater than 30 Å, as measured from the interface I towards thethicknesswise center of antiferromagnetic layer 4. These thicknessranges are the preferred thicknesses of the first and thirdantiferromagnetic layers 23 and 25 in the as-deposited state prior toheat-treatment.

Preferably, the antiferromagnetic layer 4 has a thickness which is notsmaller than 76 Å. As explained above, with reference to FIG. 4 and inconnection with the production process, each of the first and thirdantiferromagnetic layers has the minimum thickness of 3 Å, while theminimum thickness required for the second antiferromagnetic layer 24 is70 Å. Thus, the minimum required thickness of the wholeantiferromagnetic layer 4 is 76 Å.

Thus, in accordance with the present invention, the minimum thicknessrequired for antiferromagnetic layer 4 is as small as 76 Å, which issignificantly smaller than that required for conventional structures.

A hard bias layer 5 for aligning the magnetization of free magneticlayer 1, as well as a conductive layer 8, are formed on each side of thelaminate structure including lowermost underlying layer 6, topmostprotective layer 7, and the layers intermediate therebetween, as shownin FIG. 1.

Although the laminate structure employing seed layer 22, as shown inFIG. 4, has antiferromagnetic layer 4 composed of three layers whichserve to enhance the exchange coupling magnetic field, the presentinvention does not exclude the use of an antiferromagnetic layer 4having a uniform X—Mn or a uniform X+X′ composition. In such cases, itis preferred that a non-aligned state is created at at least a part ofthe interface between seed layer 22 and antiferromagnetic layer 4, orthat seed layer 22 and antiferromagnetic layer 4 are made to havedifferent lattice constants at at least a part of this interface.

More preferably, a non-aligned state is created at at least a part ofthe interface between seed layer 22 and antiferromagnetic layer 4 and,at the same time, seed layer 22 and antiferromagnetic layer 4 are madeto have different lattice constants at at least a part of thisinterface.

For instance, a single-layered antiferromagnetic layer 4 is formed of aPt₅₂Mn₄₈ alloy. The antiferromagnetic layer 4 made of such a Pt—Mn alloyexhibits a comparatively small degree of non-aligned state with respectto seed layer 22 and pinned magnetic layer 3, so that the exchangecoupling magnetic field decreases correspondingly. Nevertheless, theresistance variation ratio is improved by virtue of the presence of seedlayer 22, because the crystalline structure of at least a part ofantiferromagnetic layer 4 has a CuAu—I type face-centered cubic orderedlattice and the above-mentioned layers have such crystal orientationsthat the (111) planes are preferentially oriented in a directionparallel to antiferromagnetic layer 4 and pinned magnetic layer 3 tocreate a non-aligned state at at least a part of the interface betweenantiferromagnetic layer 4 and seed layer 22.

In this case too antiferromagnetic layer 4 and seed layer 22 may havedifferent lattice constants at at least a part of the interfacetherebetween.

In accordance with the invention, the antiferromagnetic layer 4 may becomposed of second antiferromagnetic layer 24 and thirdantiferromagnetic layer 25, with first antiferromagnetic layer 23adjacent to pinned magnetic layer 3 being omitted. In such a case, therestraint force produced by the crystalline structure of pinned magneticlayer 3 tends to provide a greater influence at the interface adjacentto pinned magnetic layer 3 to reduce the exchange coupling magneticfield. However, this problem is not critical if the interface adjacentto seed layer 22 is held in a state that avoids the influence of therestraint force produced by the crystalline structure of seed layer 22.The exchange coupling field is still greater compared to the case wherea significant influence is caused by the restraint force produced by thecrystalline structure of seed layer 22 at the interface adjacent to seedlayer 22. The proper transformation of antiferromagnetic layer 4 from adisordered lattice into an ordered lattice is ensured to a certaindegree, without impairing the large resistance variation ratio offeredby the presence of seed layer 22. In this case, antiferromagnetic layer4 has a composition modulation similar to that explained above withreference to FIG. 3; namely, it is preferred that antiferromagneticlayer 4 has a region in which the ratio of the atomic percent of theelement X or the elements X+X′ to Mn increases towards seed layer 22.Assuming a first imaginary boundary plane parallel to the interfaceadjacent to seed layer 22 on the same side of the thicknesswise centralportion of antiferromagnetic layer 4 as seed layer 22, and a secondimaginary boundary plane parallel to the interface adjacent to pinnedmagnetic layer 3 on the same side of the thicknesswise central portionas pinned magnetic layer 3, the aforementioned ratio is greater in theregion between the interface adjacent to seed layer 22 and the firstimaginary boundary plane than in the region between the first and secondimaginary boundary planes. The ratio increases linearly or non-linearlyacross the first imaginary boundary plane towards the interface adjacentto seed layer 22. It is also preferred that a non-aligned state iscreated at at least a part of the interface between seed layer 22 andantiferromagnetic layer 4.

Preferably, antiferromagnetic layer 4 has a region starting from acertain thicknesswise position towards seed layer 22, in which theatomic percent of the element X or the elements X+X′ increases towardsseed layer 22. More preferably, antiferromagnetic layer 4 further has aregion near the interface adjacent to seed layer 22, in which the atomicpercent of the element X or the elements X+X′ decreases towards seedlayer 22.

In the case where the seed layer 22 is employed, the material ofantiferromagnetic layer 4 is not limited to the X—Mn alloy or theX—Mn—X′ alloy mentioned heretofore. For instance, it is possible to usea Ni—Mn alloy that has been conventionally used as an antiferromagneticmaterial, or other Mn-free antiferromagnetic materials. The largeresistance variation ratio due to the presence of seed layer 22 isachievable even when such materials are used.

In addition, the three-layered structure of antiferromagnetic layer 4shown in FIG. 4 may be employed even when the laminate structure lacksseed layer 22, as in FIG. 2. Assuming that antiferromagnetic layer 4 inFIG. 2 is composed of three layers and that the structure is subjectedto heat-treatment, the antiferromagnetic layer 4 after heat-treatmentwill have a region in which the ratio of the atomic percent of theelement X or the elements X+X′ to Mn increases towards pinned magneticlayer 3 starting from a thicknesswise central portion, and a region inwhich the ratio of the atomic percent of the element X or the elementsX+X′ to Mn increases towards the protective layer starting from theabove-mentioned thicknesswise central portion. The crystalline structureof at least a part of antiferromagnetic layer 4 has a CuAu—I typeface-centered cubic ordered lattice. In this case too, it is preferredthat a non-aligned state is created at at least a part of the interfaceadjacent to pinned magnetic layer 3 or that antiferromagnetic layer 4and pinned magnetic layer 3 have different lattice constants at at leasta part of the above-mentioned interface. The structure shown in FIG. 2has the protective layer 7 made of a non-magnetic material such as oneor more elements selected from the group consisting of Ta, Hf, Nb, Zr,Ti, Mo, and W, formed on the side of antiferromagnetic layer 4 oppositeto pinned magnetic layer 3, so that it is conceivable that a diffusionof composition takes place between protective layer 7 andantiferromagnetic layer 4. As a result, a region in which the atomicpercent of the element X or the elements X+X′ progressively decreases isformed near the interface adjacent to protective layer 7.

Each of the laminate structures shown in FIGS. 2 to 5 can be employed ina variety of types of magnetoresistive sensors. In the laminatestructures of FIGS. 2 and 3, the antiferromagnetic layer 4 may bedeposited on the lower side of pinned magnetic layer 3, although theantiferromagnetic layer 4 is deposited on the upper side of pinnedmagnetic layer 3 in these Figures.

In such a case, the exchange coupling film is formed by sequentiallydepositing, starting from the lower side, second antiferromagnetic layer15, first antiferromagnetic layer 14, and pinned magnetic layer 3. Thethickness requirements for first and second antiferromagnetic layers 14and 15 are the same as those described above with reference to FIG. 2.

The structure having antiferromagnetic layer 4 formed on the lower sideof pinned magnetic layer 3 can be used as, for example, a single-spinvalve type magnetoresistive sensor, as shown in FIG. 6.

The single-spin valve type magnetoresistive sensor shown in FIG. 6 has alaminate structure composed of an underlying layer 6, anantiferromagnetic layer 4, a pinned magnetic layer 3, a non-magneticintermediate layer 2, a free magnetic layer 1, and a protective layer 7which are deposited sequentially from the bottom up, and has a hard biaslayer 5 and a conductive layer 8 formed on each side of the laminatestructure.

In the production of the single-spin valve type magnetoresistive sensorof FIG. 6, the antiferromagnetic layer 4 may be deposited to have athree-layered structure similar to that explained above with referenceto FIG. 4.

More specifically, the third antiferromagnetic layer 25, the secondantiferromagnetic layer 24 and the first antiferromagnetic layer 23 areformed in this order on underlying layer 6. Materials, compositions andthicknesses of these antiferromagnetic layers may be the same as thosedescribed above in connection with FIG. 4.

A subsequent heat-treatment causes diffusion of compositions betweenthese antiferromagnetic layers, so that the heat-treatedantiferromagnetic layer 4 has a region in which the ratio of the atomicpercent of the element X or the elements X+X′ to Mn progressivelyincreases towards pinned magnetic layer 3 starting from a thicknesswisecentral portion of antiferromagnetic layer 4, and a region in which theratio of the atomic percent of the element X or the elements X+X′ to Mnprogressively increases towards underlying layer 6 starting from theabove-mentioned thicknesswise central portion. The crystalline structureof at least a part of the antiferromagnetic layer 4 has a CuAu—I typeface-centered cubic ordered lattice. Preferably, a non-aligned state iscreated at at least a part of the interface adjacent to pinned magneticlayer 3 or, alternatively, both layers on this interface employdifferent lattice constants.

The methods of forming antiferromagnetic layer 4 described above are notexclusive. For example, it may be formed by varying the sputtering gaspressure while using the same target, so that the atomic percent of theelement X or the elements X+X′ is progressively changed in thethicknesswise direction.

In the laminate structures shown in FIGS. 4 and 5 having seed layer 22,the antiferromagnetic layer 4 may be deposited on the upper side ofpinned magnetic layer 3, although antiferromagnetic layer 4 is depositedon the lower side of pinned magnetic layer 3 in these Figures. Such alaminate structure can be used as a single-spin valve typemagnetoresistive sensor of the type shown in FIG. 1.

The laminate structure is formed by sequentially depositing anunderlying layer 6, a free magnetic layer 1, a non-magnetic intermediatelayer 2, a pinned magnetic layer 3, an antiferromagnetic layer 4, a seedlayer 22, and a protective layer 7, with a hard bias layer 5 and aconductive layer formed at each side of the laminate structure.Requirements concerning the crystalline structure and material of seedlayer 22 are the same as those described above with reference to FIGS. 4and 5.

FIGS. 7 and 8 are sectional views of different forms of the single-spinvalve type magnetoresistive sensor in accordance with the presentinvention.

Referring to FIG. 7, an underlying layer 6, an antiferromagnetic layer4, a pinned magnetic layer 3, a non-magnetic intermediate layer 2, and afree magnetic layer 1 are sequentially deposited from the bottom up.Thus, antiferromagnetic layer 4 is formed on the lower side of pinnedmagnetic layer 3 in this embodiment.

In the production of this magnetoresistive sensor, secondantiferromagnetic layer 15 and first antiferromagnetic layer 14 aredeposited on underlying layer 6, so as to form antiferromagnetic layer4. Pinned magnetic layer 3 is formed on antiferromagnetic layer 4.Alternatively, antiferromagnetic layer 4 may have a three-layeredstructure such as that described above with reference to FIG. 4.Preferably, each of first antiferromagnetic layer 14 and secondantiferromagnetic layer 15 is an X—Mn alloy (X is one or more elementsselected from the group consisting of Pt, Pd, Ir, Rh, Ru, and Os),preferably a Pt—Mn alloy, or an X—Mn—X′ alloy (X′ is one or moreelements selected from the group consisting of Ne, Ar, Kr, Xe, Be, B, C,N, Mg, Al, Si, P, Ti, V, Cr, Fe, Co, Ni, Cu, Zn, Ga, Ge, Zr, Nb, Mo, Ag,Cd, Sn, Hf, Ta, W, Re, Au, Pb and a rare earth element).

In accordance with the present invention, it is preferred that anon-aligned state is created at at least a part of the interface betweenfirst antiferromagnetic layer 14 and pinned magnetic layer 3. The secondantiferromagnetic layer 15 is formed of an antiferromagnetic materialhaving a composition approximating an ideal composition for facilitatingtransformation from a disordered lattice structure into an orderedlattice structure upon heat-treated. The requirements concerning thecomposition ratios of the element X or the elements X+X′ and thethickness of first antiferromagnetic layer 14 and secondantiferromagnetic layer 15 are the same as those explained above withreference to FIG. 2.

The process for forming antiferromagnetic layer 4 described above is notexclusive. The first antiferromagnetic layer 4 may be formed by varyingthe sputter gas pressure while using the same target, so that the atomicpercent of the element X or the elements X+X′ is progressively changedin the thicknesswise direction.

A heat-treatment is conducted after deposition of antiferromagneticlayer 4. The heat-treatment causes a proper transformation from adisordered lattice structure into an ordered lattice structure in thesecond antiferromagnetic layer 15, as well as a diffusion ofcompositions at the boundary between first antiferromagnetic layer 14and second antiferromagnetic layer 15. As a result, transformation froma disordered lattice structure into ordered lattice structure isproperly effected in the first antiferromagnetic layer 14.

Preferably, the ratio of the atomic percent of the element X or theelements X+X′ in the state after heat-treatment increases towards pinnedmagnetic layer 3, with the crystalline structure of at least a part ofantiferromagnetic layer 4 having a CuAu—I type face-centered cubicordered lattice, and with a non-aligned state being created at at leasta part of the interface between antiferromagnetic layer 4 and pinnedmagnetic layer 3. It is also preferred that pinned magnetic layer 3 andantiferromagnetic layer 4 have different lattice constants or differentcrystal orientations at the interface therebetween.

When antiferromagnetic layer 4 has been deposited to have athree-layered structure, as shown in FIG. 4, or when antiferromagneticlayer 4 has been deposited such that the composition ratio of theelement X or the elements X+X′ progressively decreases towards thethicknesswise central portion from both interfaces on antiferromagneticlayer 4, the heat-treated antiferromagnetic layer 4 has a region inwhich the ratio of the atomic percent of the element X to Mnprogressively increases towards pinned magnetic layer 3 starting from athicknesswise central portion of the antiferromagnetic layer 4. Inaddition, the heat-treated antiferromagnetic layer 4 has a region inwhich the ratio of the atomic percent of the element X to Mnprogressively increases towards underlying layer 6 starting from theabove-mentioned thicknesswise central portion of antiferromagnetic layer4. The crystalline structure of at least a part of antiferromagneticlayer 4 has a CuAu—I type face-centered cubic ordered lattice and,preferably, a non-aligned state is created at at a least part of theinterface adjacent to pinned magnetic layer 3. Alternatively, bothlayers are made to have different lattice constants or different crystalorientations at the interface therebetween.

As shown in FIG. 7, segments 16 of the exchange bias layer are formed onfree magnetic layer 1, leaving therebetween a space corresponding to thetrack width Tw in the track width direction.

The exchange bias layer 16 is formed from an X—Mn alloy (X is one ormore elements selected from the group consisting of Pt, Pd, Ir, Rh, Ru,and Os), preferably a Pt—Mn alloy, or from an X—Mn—X′ alloy (X′ is oneor more elements selected from the group consisting of Ne, Ar, Kr, Xe,Be, B, C, N, Mg, Al, Si, P, Ti, V, Cr, Fe, Co, Ni, Cu, Zn, Ga, Ge, Zr,Nb, Mo, Ag, Cd, Sn, Hf, Ta, W, Re, Au, Pb and a rare earth element).

Deposition of exchange bias layer 16 involves forming a firstantiferromagnetic layer 14 on free magnetic layer 1, and forming asecond antiferromagnetic layer 15 on first antiferromagnetic layer 14.First antiferromagnetic layer 14 and second antiferromagnetic layer 15are the same as those shown in FIG. 2. The first antiferromagnetic layer14 has a greater composition ratio of the element X or the elements X+X′than the second antiferromagnetic layer 15 and, in addition, the secondantiferromagnetic layer 15 is formed of an antiferromagnetic materialhaving a composition approximating an ideal composition for transformingeasily from a disordered lattice structure into an ordered latticestructure upon heat-treatment.

As a result of the above-described heat-treatment, the exchange biaslayer 16 is properly transformed from a disordered lattice structureinto an ordered lattice structure, without undergoing the restraintforce produced by the crystalline structure of pinned magnetic layer 3at the interface adjacent to free magnetic layer 1. As a result, anexchange coupling magnetic field is generated at the interface betweenexchange bias layer 16 and free magnetic layer 1.

After heat treatment, the exchange bias layer 16 has a region in whichthe ratio of the atomic percent of the element X or elements X+X′ to Mnincreases towards free magnetic layer 1, the crystalline structure of atleast a part of exchange bias layer 16 has a CuAu—I type face-centeredcubic ordered lattice and, preferably, a non-aligned state is created atat least a part of the interface adjacent to free magnetic layer 1.

The exchange bias layer 16 may be formed to have a three-layeredstructure such as that described above with reference to FIG. 4. In sucha case, exchange bias layer 16 has a region in which the ratio of theatomic percent of the element X or elements X+X′ to Mn increases towardsfree magnetic layer 1 starting from a thicknesswise central portion ofexchange bias layer 16, and a region in which the ratio of the atomicpercent of the element X or elements X+X′ to Mn increases in thedirection away from free magnetic layer 1 starting from theabove-mentioned thicknesswise central portion. In addition, thecrystalline structure of at least a part of the exchange bias layer 16has a CuAu—I type face-centered cubic ordered lattice. Preferably, anon-aligned state is created at at least a part of the interfaceadjacent to free magnetic layer 1. Alternatively, both layers on theabove-mentioned interface have different lattice constants or differentcrystal orientations.

Both end portions of free magnetic layer 1 are formed into a singlemagnetic domain in the X direction by the effect of the exchangecoupling magnetic field acting between exchange bias layer 16 and freemagnetic layer 1. The region of free magnetic layer 1 extending over thewidth Tw corresponding to the track width has been properly aligned inthe X direction to such a degree as to be sensitive to external magneticfields.

In the single-spin valve type magnetoresistive sensor produced by thedescribed process, the magnetization of free magnetic layer 1 at theregion of the track width Tw changes from the X direction to the Ydirection under the influence of an external magnetic field applied inthe Y direction. Electric resistance is changed based on therelationship between the change of the magnetization in free magneticlayer 1 and the fixed direction (Y direction) of magnetization of pinnedmagnetic layer 3. The change in the electrical resistance causes achange in voltage, thus enabling sensing of a magnetic field leakingfrom a recording medium.

The single-spin valve type magnetoresistive sensor of FIG. 7 may have aseed layer 22 such as that explained above with reference to FIGS. 4 and5.

In such a case, seed layer 22 is interposed between antiferromagneticlayer 4 and underlying layer 6. The seed layer has a crystallinestructure primarily constituted by face-centered cubic crystals, withthe (111) plane preferentially oriented in a direction parallel to theinterface adjacent to antiferromagnetic layer 4. The use of such a seedlayer 22 permits antiferromagnetic layer 4 and free magnetic layer 1, aswell as intervening layers, to be aligned such that their (111)faces arepreferentially oriented, thus allowing growth of large crystal grains.It is therefore possible to increase the ratio of the resistancevariation.

The requirements concerning the material of seed layer 22 and thestructure of antiferromagnetic layer 4 are the same as those describedabove with reference to FIGS. 4 and 5.

The seed layer 22 may be formed on the exchange bias layer 16.

FIG. 8 shows a single-spin valve type magnetoresistive sensor having alaminate structure deposited in an order reverse to that of themagnetoresistive sensor of FIG. 7.

Referring to FIG. 8, segments 16 of the exchange bias layer are formedso as to be spaced apart from each other by a distance corresponding tothe track width Tw. The vacancy between segments 16 of the exchange biaslayer is filled with an insulating layer 17 made of an insulatingmaterial such as SiO₂ or Al₂O₃.

A free magnetic layer 13 is formed to overlie exchange bias layer 16 andinsulating layer 17. In this embodiment too, the exchange bias layer 16as deposited (i.e., prior to heat-treatment), has a laminate structurecomposed of a first antiferromagnetic layer 14 and a secondantiferromagnetic layer 15.

More specifically, the second antiferromagnetic layer 15 is depositedfirst, followed by the first antiferromagnetic layer 14. The widthwisecentral portion of first antiferromagnetic layer 14 and secondantiferromagnetic layer 15 is removed by etching for example. Thevacancy between segments 16 thus obtained is then filled with insulatinglayer 17, followed by deposition of the free magnetic layer 13 overlyingexchange bias layer 16 and insulating layer 17. The firstantiferromagnetic layer 14 constituting part of exchange bias layer 16has a greater composition ratio of the element X or the elements X+X′than the second antiferromagnetic layer 15 which constitutes the otherpart of exchange bias layer 16. In addition, second antiferromagneticlayer 15 is formed of an antiferromagnetic material having a compositionapproximating an ideal composition for facilitating transformation fromthe disordered lattice structure into an ordered lattice structure. Therequirement concerning the composition ratios of the element X or theelements X+X′ and the thicknesses of the first antiferromagnetic layer14 and the second antiferromagnetic layer 15 are the same as thoseexplained above with reference to FIG. 2.

The laminate structure up to free magnetic layer 1 is subjected to aheat-treatment after deposition. As a result of heat-treatment, theexchange bias layer 16 is properly transformed to change its structurefrom a disordered lattice into an ordered lattice without beinginfluenced by the restraint force of the crystalline structure of freemagnetic layer 1 at the interface adjacent to free magnetic layer 1. Anexchange coupling magnetic field is generated at the boundary betweenexchange bias layer 16 and free magnetic layer 1. The exchange biaslayer 16 after heat-treatment has a region in which the ratio of theatomic percent of the element X or elements X+X′ to Mn increases towardsfree magnetic layer 1. The crystalline structure of at least a part ofexchange bias layer 16 has a CuAu—I type face-centered cubic orderedlattice and, preferably, a non-aligned state is created at at least apart of the interface adjacent to free magnetic layer 1. Both endportions of free magnetic layer 1 are formed into a single magneticdomain in the X direction by the effect of the above-mentioned exchangecoupling magnetic field. The region of free magnetic layer 1 extendingover the width Tw corresponding to the track width has been properlyaligned in the X direction to such a degree as to be sensitive toexternal magnetic fields. The exchange bias layer 16 may be formed tohave a three-layered structure such as that described above withreference to FIG. 4. Tn such a case, the exchange bias layer 16 has aregion in which the ratio of the atomic percent of the element X orelements X+X′ to Mn increases towards free magnetic layer 1 startingfrom a thicknesswise central portion of exchange bias layer 16, and aregion in which the ratio of the atomic percent of the element X orelements X+X′ to Mn increases in the direction away from free magneticlayer 1 starting from the above-mentioned thicknesswise central portion.In addition, the crystalline structure of at least a part of theexchange bias layer 16 has a CuAu—I type face-centered cubic orderedlattice. Preferably, a non-aligned state is created at at least a partof the interface adjacent to free magnetic layer 1. Alternatively, bothlayers on the above-mentioned interface have different lattice constantsor different crystal orientations.

Then, non-magnetic intermediate layer 2, pinned magnetic layer 3,antiferromagnetic layer 4 and protective layer 7 are depositedsequentially free magnetic layer 1.

In the deposition process prior to heat-treatment, the firstantiferromagnetic layer 14 is formed on pinned magnetic layer 3 and thensecond antiferromagnetic layer 15 is formed on first antiferromagneticlayer 14. In the as-deposited state, first antiferromagnetic layer 14has a greater composition ratio of the element X or the element X+X′than second antiferromagnetic layer 15. Preferably, a non-aligned stateis created at at least a part of the interface adjacent to pinnedmagnetic layer 3. In addition, the second antiferromagnetic layer 15 isformed from an antiferromagnetic material having a compositionapproximating an ideal composition for facilitating transformation froma disordered lattice structure into an ordered lattice structure uponheat-treatment.

The heat-treatment is executed after deposition of antiferromagneticlayer 14 and second antiferromagnetic layer 15. As a result ofheat-treatment, antiferromagnetic layer 4 is properly transformed fromits disordered lattice structure into an ordered lattice structure,without being influenced by the restraint force produced by thecrystalline structure of pinned magnetic layer 3 at the interfaceadjacent to pinned magnetic layer 3. As a result, an exchange couplingmagnetic field is generated at the interface between antiferromagneticlayer 4 and pinned magnetic layer 3. The exchange coupling magneticfield serves to fix the magnetization of pinned magnetic layer 3 in thedirection Y shown in the drawings.

Since the influence of the restraint force produced by the crystallinestructure of pinned magnetic layer 3 is diminished at the interfaceadjacent to pinned magnetic layer 3 during heat-treatment, and since thefirst antiferromagnetic layer 4 has a composition approximating an idealcomposition for facilitating transformation from a disordered latticestructure into an ordered lattice structure, a greater exchange couplingmagnetic field than in conventional devices, specifically 7.9×10⁴ A/m orgreater, is produced between first antiferromagnetic layer 4 and pinnedmagnetic layer 3. In the deposition process, antiferromagnetic layer 4may be formed to have a three-layered structure such as that describedabove with reference to FIG. 4. In such a case, the antiferromagneticlayer 4 has a region in which the ratio of the atomic percent of theelement X or elements X+X′ to Mn increases towards pinned magnetic layer3 starting from a thicknesswise central portion of antiferromagneticlayer 4, and a region in which the ratio of the atomic percent of theelement X or elements X+X′ to Mn increases towards protective layer 7starting from the above-mentioned thicknesswise central portion. Inaddition, the crystalline structure of at least a part ofantiferromagnetic layer 4 has a CuAu—I type face-centered cubic orderedlattice. Preferably, a non-aligned state is created at at least a partof the interface adjacent to pinned magnetic layer 3. Alternatively,both layers on the above-mentioned interface have different latticeconstants or different crystal orientations.

This embodiment also may employ a seed layer 22. Such a seed layer isformed between antiferromagnetic layer 4 and protective layer 7. It ispossible to enhance the exchange coupling magnetic field by the use ofseed layer 22. The requirements concerning the material of seed layer 22and the structure of antiferromagnetic layer 4 are the same as thosedescribed above with reference to FIGS. 4 and 5.

Preferably, the seed layer 22 is formed on the lower side of exchangebias layer 16, as shown in FIG. 8. By forming seed layer 22, it ispossible to orderly align the crystal orientation of exchange bias layer16, making it possible to properly generate an exchange couplingmagnetic field between free magnetic layer 1 and exchange bias layer 16.

FIG. 9 is a sectional view showing the structure of a dual-spin valvetype magnetoresistive sensor in accordance with the present invention.

As is shown in FIG. 9, an underlying layer 6, an antiferromagnetic layer4, a pinned magnetic layer 3, a non-magnetic intermediate layer 2, and afree magnetic layer 1 are sequentially deposited from the bottom up.Further, another non-magnetic intermediate layer 2, another pinnedmagnetic layer 3, another antiferromagnetic layer 4 and a protectivelayer 7 are sequentially deposited on free magnetic layer 1.

A hard bias layer 5 and a conductive layer 8 are formed on each side ofthe laminate structure starting from underlying layer 6 and terminatingin protective layer 7. All of these layers are formed of materials thatare the same as those described above with reference to FIGS. 1 to 7.

A description will now be given of the production process, withreference to FIG. 10. In the deposition process, each of the twoantiferromagnetic layers 4 is formed to have a two-layered structurecomposed of a first antiferromagnetic layer 14 and a secondantiferromagnetic layer 15. The first antiferromagnetic layer 14 isformed in contact with pinned magnetic layer 3, and the secondantiferromagnetic layer 15 is formed in contact with firstantiferromagnetic layer 14. Each of the first antiferromagnetic layer 14and the second antiferromagnetic layer 15 is formed from an X—Mn alloyor an X—Mn—X′ alloy, as described above.

In the as-deposited state, the first antiferromagnetic layer 14 has agreater composition ratio of the element X or the element X+X′ than thesecond antiferromagnetic layer 15. Preferably, a non-aligned state iscreated at at least a part of the interface adjacent to pinned magneticlayer 3. In addition, the second antiferromagnetic layer 15 is formedfrom an antiferromagnetic material having a composition approximating anideal composition for facilitating transformation from a disorderedlattice structure to an ordered lattice structure upon heat-treatment.Requirements for the composition ratios of the element X or the elementsX+X′, and the thicknesses of the respective antiferromagnetic layers arethe same as those described above with reference to FIG. 2.

The heat-treatment is executed after deposition of the antiferromagneticlayer 14 and second antiferromagnetic layer 15. As a result ofheat-treatment, antiferromagnetic layer 4 is properly transformed tochange its disordered lattice structure into an ordered latticestructure, without being influenced by the restraint force produced bythe crystalline structure of pinned magnetic layer 3 at the interfaceadjacent to pinned magnetic layer 3. An exchange coupling magnetic fieldgenerated at the above-mentioned interface serves to fix themagnetization of pinned magnetic layer 3 in the direction Y shown in thedrawings.

Since the first antiferromagnetic layer 14 is formed of a suitablematerial free from the influence of the restraint force produced by thecrystalline structure of pinned magnetic layer 3 at the interfaceadjacent to pinned magnetic layer 3, and since the secondantiferromagnetic layer 15 is formed from a material having acomposition approximating an ideal composition for facilitatingtransformation from a disordered lattice structure into an orderedlattice structure, the transformation from a disordered latticestructure into an ordered lattice structure is properly effected byheat-treatment, while a non-aligned state is maintained betweenantiferromagnetic layer 4 and pinned magnetic layer 3. As a result, agreater exchange coupling magnetic field than in conventional devicescan be obtained. Specifically, an exchange coupling magnetic field of7.9×10⁴ A/m or greater is expected in accordance with the presentinvention.

FIG. 11 shows the state of the structure after heat-treatment. Theantiferromagnetic layer 4 shown in FIG. 11 has a region in which theratio of the atomic percent of the element X or elements X+X′ to Mnincreases towards pinned magnetic layer 3, and the crystalline structureof at least a part of antiferromagnetic layer 4 has a CuAu—I typeface-centered cubic ordered lattice. Preferably, a non-aligned state iscreated at at least a part of the interface adjacent to pinned magneticlayer 3. Both layers on the above-mentioned interface preferably havedifferent lattice constants or different crystal orientations, in orderthat the non-aligned state is maintained.

The presence of the region in antiferromagnetic layer 4 in which theratio of the atomic percent of the element X or elements X+X′ to Mnincreases towards pinned magnetic layer 3 is attributed to the fact thatantiferromagnetic layer 4 is deposited to have a laminate structurecomposed of first antiferromagnetic layer 14 having a large atomicpercent of the element X or the elements X+X′ and secondantiferromagnetic layer 15. More specifically, although theheat-treatment causes diffusion of composition between firstantiferromagnetic layer 14 and second antiferromagnetic layer 15,diffusion does not proceed to such an extent as to provide a uniformcomposition of the entire antiferromagnetic layer 4. The region that wasconstituted by the first antiferromagnetic layer 14 still has a portionwhere the composition ratio of the element X or the elements X+X′ isgreater than in the region that was constituted by the secondantiferromagnetic layer 15. As a result, a region is formed in which theratio of the atomic percent of the element X or elements X+X′ to Mnincreases towards pinned magnetic layer 3.

While it is not the Applicants' desire to be bound by a particulartheory, it is believed that the antiferromagnetic layer 4 has a regionnear the interface adjacent to pinned magnetic layer 3, in which thecomposition ratio of the element X or the elements X+X′ in theantiferromagnetic layer 4 decreases towards pinned magnetic layer 3.This is attributable to the diffusion of compositions betweenantiferromagnetic layer 4 and pinned magnetic layer 3 caused byheat-treatment. Likewise, the diffusion of composition takes placebetween antiferromagnetic layer 4 and underlying layer 6, and betweenantiferromagnetic layer 4 and protective layer 7. It is thereforeunderstood that antiferromagnetic layer 4 also has a region near theinterface adjacent to underlying layer 6, as well as a region near theinterface adjacent to protective layer 7, in which the composition ratioof the element X or the elements X+X′ in antiferromagnetic layer 4decreases towards the interface.

Requirements concerning the composition ratios of the element X or theelements X+X′ of antiferromagnetic layer 4 at the interface adjacent topinned magnetic layer 3 or at the side opposite to this interface, thethickness of antiferromagnetic layer 4, and so forth, are the same asdescribed above in connection with FIG. 3.

This embodiment also may employ a seed layer 22. The production processis shown in FIG. 12. Seed layer 22 is formed on underlying layer 6, andan antiferromagnetic layer 4 having a three-layered structure isdeposited on seed layer 22. The structure of antiferromagnetic layer 4is the same as that described above with reference to FIG. 10.

The antiferromagnetic layer 4 formed on seed layer 22 has a thirdantiferromagnetic layer 25 adjacent to seed layer 22, a firstantiferromagnetic layer 23 adjacent to pinned magnetic layer 3, and asecond antiferromagnetic layer 24 interposed between firstantiferromagnetic layer 23 and third antiferromagnetic layer 25.

As described above with reference to FIG. 4, each of the first throughthird antiferromagnetic layers is formed from an X—Mn alloy or anX—Mn—X′ alloy, wherein the composition ratio of the element X or theelements X+X′ in the second antiferromagnetic layer 24 is determined tobe smaller than in the remaining two antiferromagnetic layers. Suchadjustment of the composition ratio makes it possible to create anon-aligned state at at least a part of the interface between seed layer22 and third antiferromagnetic layer 25, as well as at the interfacebetween pinned magnetic layer 3 and third antiferromagnetic layer 25.The layers facing each other across each of these interfaces may havedifferent lattice constants.

The seed layer 22 has face-centered cubic crystals with the (111) planespreferentially oriented in the direction parallel to the interfaceadjacent to pinned magnetic layer 3. The layers formed on this seedlayer have crystalline structures in which their (111) planes areoriented in the direction parallel to the above-mentioned interface. Thematerial of seed layer 22 may be similar to that described above withreference to FIG. 4, although the material preferably has non-magneticproperties and a high specific resistance.

As will be seen from FIG. 12, antiferromagnetic layer 4 formed abovefree magnetic layer 1 has a two-layered structure, as in the case of thestructure described above with reference to FIG. 2. This, however, isnot essential, and the antiferromagnetic layer 4 formed above freemagnetic layer 1 may have a three-layered structure as in the case ofthe antiferromagnetic layer 4 which is formed below free magnetic layer1.

FIG. 13 schematically shows the dual-spin valve type magnetoresistivesensor obtained by heat-treatment.

Since second antiferromagnetic layers 24 and 15 have compositions apt tobe transformed into ordered lattice structures, transformation intoordered lattice structures is commenced in the second antiferromagneticlayer 24 of the first antiferromagnetic layer 4 below free magneticlayer 1, and in the second antiferromagnetic layer 15 of theantiferromagnetic layer 4 above free magnetic layer 1. As a result ofdiffusions of compositions caused by heat-treatment, transformation alsoproceeds in other layers, while the non-aligned state is maintained.Thus, a greater exchange coupling magnetic field than in conventionaldevices can be achieved.

As a result of the above-described diffusions of compositions, theantiferromagnetic layer 4 beneath free magnetic layer 1 has a region inwhich the ratio of the atomic percent of the element X or the elementsX+X′ to Mn increases towards pinned magnetic layer 3, as well as aregion in which this ratio increases towards seed layer 22. At the sametime, the crystalline structure of at least a part of thisantiferromagnetic layer 4 has a CuAu—I type face-centered crystallinestructure. Preferably, a non-aligned state is created at at least a partof the interface adjacent to seed layer 22, as well as at least a partof the interface adjacent to pinned magnetic layer 3.

Meanwhile, the antiferromagnetic layer 4 above free magnetic layer 1 hasa region in which the ratio of the atomic percent of the element X orthe elements X+X′ to Mn increases towards pinned magnetic layer 3. Atthe same time, the crystalline structure of at least a part of thisantiferromagnetic layer 4 has a CuAu—I type face-centered crystallinestructure. Preferably, a non-aligned state is created at at least a partof the interface adjacent to pinned magnetic layer 3. Theantiferromagnetic layer 4 formed above free magnetic layer 1 also has acrystal orientation in which the (111) planes are preferentiallyaligned.

In the antiferromagnetic layer 4 below free magnetic layer 1, it isbelieved that diffusion of composition takes place at the interfaceadjacent to seed layer 22 and at the interface adjacent to pinnedmagnetic layer 3, so that regions exist near the interface adjacent toseed layer 22 and near the interface adjacent to the pinned magneticlayer 3, respectively, in which the atomic percent of the element X orthe elements X+X′ in antiferromagnetic layer 4 decreases towards therespective interfaces. The presence of such regions indicates thatantiferromagnetic layer 4 has been properly transformed into an orderedlattice structure at the interface adjacent to seed layer 22 and at theinterface adjacent to pinned magnetic layer 3, thereby providing a largeexchange coupling magnetic field.

While it is not the Applicants' desire to be bound by a particulartheory, it is believed that in the antiferromagnetic layer 4 formedabove free magnetic layer 1, a diffusion of compositions takes place atthe interface adjacent to pinned magnetic layer 3. As a result, a regionexists near the interface adjacent to pinned magnetic layer 3, in whichthe atomic percent of the element X or the elements X+X′ inantiferromagnetic layer 4 decreases towards the above-mentionedinterface. It is also conceivable that a diffusion of composition takesplace at the boundary between antiferromagnetic layer 4 and theprotective layer which is formed, for example, of Ta. If such adiffusion has taken place, a region exists in antiferromagnetic layer 4near the interface adjacent to protective layer 7, in which the atomicpercent of the element X or the elements X+X′ in the antiferromagneticlayer 4 decreases towards this interface.

The presence of seed layer 22 serves to promote preferential orientationof the (111) planes in parallel with the film planes, and to increasethe sizes of the crystal grains in antiferromagnetic layer 4 below freemagnetic layer 1 and in antiferromagnetic layer 4 above free magneticlayer 1, as well as in the layers intervening between these twoantiferromagnetic layers 4. It is therefore possible to obtain a greaterexchange magnetic field and a greater ratio of resistance variation thanin conventional devices.

In order to better improve the ratio of resistance variation, seed layer22 is preferably formed between underlying layer 6 and theantiferromagnetic layer 4 below free magnetic layer 1, as shown in FIGS.12 and 13. The seed layer 22, however, may be formed between protectivelayer 7 and antiferromagnetic layer 4 above free magnetic layer 1.

FIGS. 14 and 15 are sectional views of AMR magnetoresistive sensorsembodying features of the present invention.

Referring to FIG. 14, a soft magnetic layer (SAL layer) 18, anon-magnetic layer (SHUNT layer) 19, and a magnetoresistive layer (MRlayer) are successively deposited.

By way of example, soft magnetic layer 18 is formed of a Fe—Ni—Nb alloy,while non-magnetic layer 19 is made from a Ta film. The magnetoresistivelayer 20 is formed of a Ni—Fe alloy.

Segments 21 of an exchange bias layer (antiferromagnetic layer) spacedfrom each other in the the direction of the track width (X direction) bya distance corresponding to the track width Tw, are formed on both endportions of magnetoresistive layer 20. Although not shown, a conductivelayer is formed, for example, on the segments 21 of the exchange biaslayer.

Referring to FIG. 15, segments 21 of the exchange bias layer are formedso as to be spaced apart from each other in the track width direction (Xdirection) by a distance corresponding to the track width Tw. Thevacancy between these segments 21 of the exchange bias layer is filledwith an insulating layer 26 made of an insulating material such as SiO₂or Al₂O₃.

The exchange bias layer 21 and the insulating layer 26 are overlain bythe magnetoresistive layer (MR layer) 20, the non-magnetic layer (SHUNTlayer) 19 and the soft magnetic layer (SAL layer) 18.

In the production process, the exchange bias layer 21 is deposited tohave a two-layered structure composed of first antiferromagnetic layer14 and second antiferromagnetic layer 15.

The first antiferromagnetic layer 14 is formed in contact withmagnetoresistive layer 20, and the second antiferromagnetic layer 15 isformed on magnetoresistive layer 20 with first antiferromagnetic layer14 intervening therebetween.

As described above in connection with FIG. 2, the firstantiferromagnetic layer 14 has a greater composition ratio of theelement X or the element X+X′ than the second antiferromagnetic layer15. Preferably, a non-aligned state is created at at least a part of theinterface adjacent to magnetoresistive layer 20, and secondantiferromagnetic layer 15 is formed of an antiferromagnetic materialhaving a composition approximating an ideal composition for facilitatingtransformation from the disordered lattice structure into an orderedlattice structure upon heat-treatment. The composition ratios of theelement X or the elements X+X′ in first antiferromagnetic layer 14 andsecond antiferromagnetic layer 15, as well as the thicknesses of theseantiferromagnetic layers, are the same as those described above withreference to FIG. 2.

As a result of heat-treatment, the exchange bias layer 21 is properlytransformed from the disordered lattice structure into an orderedlattice structure, while the non-aligned state is maintained at theinterface adjacent to magnetoresistive layer 20. As a result, anexchange coupling magnetic field is produced at the interface betweenexchange bias layer 21 and magnetoresistive layer 20.

Since the first antiferromagnetic layer 14 is formed of a suitablematerial free from the influence of the restraint force produced by thecrystalline structure of magnetoresistive layer 20 at the interfaceadjacent to layer 20, and since the second antiferromagnetic layer 15 isformed from a material having a composition approximating an idealcomposition for facilitating transformation from a disordered latticestructure into an ordered lattice structure, the transformation from adisordered lattice structure into an ordered lattice structure isproperly effected by heat-treatment, while a non-aligned state ismaintained between antiferromagnetic layer 4 and magnetoresistive layer20. As a result, a greater exchange coupling magnetic field than inconventional devices can be obtained. Specifically, an exchange couplingmagnetic field of 7.9

10⁴ A/m or greater is expected in accordance with the present invention.

In the deposition process, exchange bias layer 21 may be formed of athree-layered structure as in the embodiment described above withreference to FIG. 4. A first antiferromagnetic layer 23 is formed onmagnetoresistive layer 20. A second antiferromagnetic layer 24 and athird antiferromagnetic layer 25 are deposited sequentially to overliefirst antiferromagnetic layer 23. The composition ratio of the element Xor the elements X+X′ is determined to be smaller in the secondantiferromagnetic layer 24 than in the first and third antiferromagneticelements 23 and 25. Preferably, a non-aligned state is created at atleast a part of the interface between first antiferromagnetic layer 23and magnetoresistive layer 20. Alternatively, both layers facing thisinterface are made to have different lattice constants or differentcrystal orientations at the interface.

When heat-treatment is effected on the exchange bias layer 21 thusformed, transformation into an ordered lattice structure is commenced insecond antiferromagnetic layer 24, followed by transformation intoordered lattice structures in first antiferromagnetic layer 23 and thirdantiferromagnetic layer 25 due to diffusions of compositions.Consequently, the heat-treated exchange bias layer 21 has a region inwhich the ratio of atomic percent of the element X to Mn increasestowards magnetoresistive layer 20 starting from a thicknesswise centralportion of exchange bias layer 21, and a region in which the ratio ofatomic percent of the element X to Mn increases in the direction awayfrom magnetoresistive layer 20 starting from the above-mentionedthicknesswise central portion.

Requirements concerning the compositions of the first through thirdantiferromagnetic layers 23, 24 and 25 are the same as described abovewith reference to FIG. 4. The composition and thickness of exchange biaslayer 21 after heat-treatment are the same as those of antiferromagneticlayer 4 shown in FIG. 5.

This embodiment also can employ a seed layer 22. In particular, the useof the seed layer 22 in the structure shown in FIG. 15 is preferred.When exchange bias layer 21 is formed on the lower side ofmagnetoresistive layer 20, seed layer 22 is formed on the lower side ofexchange bias layer 21. The structure shown in FIG. 14 also may employseed layer 22. In such a case, seed layer 22 is formed on the upper sideof exchange bias layer 21. The use of such a seed layer 22 enhances theratio of resistance variation. Requirements regarding the crystallinestructure and material of seed layer 22, as well as the material,composition and film thickness of the exchange bias layer 21, are thesame as those shown in FIGS. 4 and 5.

In each of the AMR devices shown in FIGS. 14 and 15, the regions E ofmagnetoresistive layer 20 are formed into a single magnetic domain inthe X direction, due to the effect of the exchange coupling magneticfield produced at the interface between exchange bias layer 21, 21 andmagnetoresistive layer 20. This causes the magnetization of the region Dof magnetoresistive layer 20 to be aligned in the X direction. Amagnetic field which is produced when a sense current flows throughmagnetoresistive layer 20 is applied to soft magnetic layer 18, so thata lateral bias magnetic field Y is applied to the region D ofmagnetoresistive layer 20 by the static magnetic coupling energyproduced by soft magnetic layer 18. Thus, the lateral magnetic field isapplied to the region D of the magnetoresistive layer 20 that has beenformed into a single magnetic domain in the X direction. As a result,the region D of magnetoresistive layer 20 exhibits a linear change ofresistance in response to a change in magnetic field, thus achievinglinear magnetoresistive characteristics (i.e., a linear H—R effectcharacteristic).

A recording medium moves in the direction Z, so that a magnetic fieldleaking in the Y direction causes a change in the electrical resistancein the region D of magnetoresistive layer 20. Such a change is sensed asa change in voltage.

FIG. 16 is a sectional view of the structure of a reading head havingany of the magnetoresistive sensors described heretofore with referenceto FIGS. 1 to 11, as viewed from the surface opposing the recordingmedium.

Numeral 40 designates a lower shield layer formed of, for example, aNi—Fe alloy, and overlain by a lower gap layer 41. A magnetoresistivesensor 42, which may be any one of those described heretofore withreference to FIGS. 1 to 15, is formed on the lower gap layer 41. Themagnetoresistive sensor 42 is overlain by an upper gap layer 43 formedthereon. An upper shield layer 44 formed, for example, of a Ni—Fe alloyis formed on the upper gap layer 43.

The lower gap layer 41 and the upper gap layer 43 are formed of aninsulating material such as SiO₂ or Al₂O₃ (alumina). The length betweenthe extremities of the lower gap layer 41 and upper gap layer 43, asshown in FIG. 16, is the gap length Gl. The reading head with a smallergap length Gl can be used at higher recording density.

As described above, the present invention makes it possible to achieve alarge exchange coupling magnetic field, even with a reduced thickness ofantiferromagnetic layer 4. It is therefore possible to reduce thethickness of the magnetoresistive sensor as compared with conventionaldevices and, therefore, to produce a thin-film magnetic head which has anarrower gap to cope with the demand for higher recording density.

EXAMPLES

The following laminate structures were formed by deposition. Sampleswere prepared in which the antiferromagnetic layer 4 was formed bydepositing two layers (first antiferromagnetic layer 14 and secondantiferromagnetic layer 15) having different composition ratios as inFIG. 2 (Examples), in which the antiferromagnetic layer 30 was depositedto have a single layer, as shown in FIG. 20 (Comparative Examples). Thesamples were then subjected to heat-treatments conducted under the sameconditions, and the exchange coupling magnetic field (Hex) and ratio ofresistance variation (ΔMR) were then measured. The heat-treatment wasconducted for more than 2 hours at temperatures not lower than 200° C.

Example 1

The laminate structure was composed of the following layers, asmentioned from the bottom layer: Underlying layer 6: Ta (50)/freemagnetic layer 1: [Ni₈₀Fe₂₀(45)/Co(5)]/non-magnetic intermediate layer2: Cu(25)/pinned magnetic layer 3: [Co(20)/Ru(8)/Co(15)]/firstantiferromagnetic layer 14: Pt₅₈Mn₄₂ (10)/second antiferromagneticlayer: Pt₅₀Mn₅₀(110)/protective layer 7: Ta (30)

Comparative Example 1

Underlying layer 6: Ta (50)/free magnetic layer 1:[Ni₈₀Fe₂₀(45)/Co(5)]/non-magnetic intermediate layer 2: Cu(25)/pinnedmagnetic layer 3: [Co(20)/Ru(8)/Co(15)]/antiferromagnetic layer 30:Pt₅₈Mn₄₂ (120)/protective layer 7: Ta(30)

Comparative Example 2

Underlying layer 6: Ta (50)/free magnetic layer 1:[Ni₈₀Fe₂₀(45)/Co(5)]/non-magnetic intermediate layer 2: Cu(25)/pinnedmagnetic layer 3: [Co(20)/Ru(8)/Co(15)]/antiferromagnetic layer 30:Pt₄₆Mn₅₄ (120)/protective layer 7: Ta(30)

Comparative Example 3

Underlying layer 6: Ta (50)/free magnetic layer 1:[Ni₈₀Fe₂₀(45)/Co(5)]/non-magnetic intermediate layer 2: Cu(25)/pinnedmagnetic layer 3: [Co(20)/Ru(8)/Co(15)]/antiferromagnetic layer 30:Pt₅₀Mn₅₀ (120)/protective layer 7: Ta(30)

Comparative Example 4

Underlying layer 6: Ta (50)/free magnetic layer 1:[Ni₈₀Fe₂₀(45)/Co(5)]/non-magnetic intermediate layer 2: Cu(25)/pinnedmagnetic layer 3: [Co(20)/Ru(8)/Co(15)]/antiferromagnetic layer 30:Pt₅₂Mn₄₈ (120)/protective layer 7: Ta(30)

Values in parentheses indicate the layer thickness in Angstroms. Thesuffixes in the representations of Ni—Fe alloys and Pt—Mn alloysrepresent composition ratios in terms of at %.

Thus, all the samples had the same laminate structure, except for thestructure of the antiferromagnetic layer. The thickness of theantiferromagnetic layers was 120 Å in all samples. In Example 1, thisthickness is the sum of the thicknesses of first antiferromagnetic layer14 and second antiferromagnetic layer 15.

TABLE 1 Example 1 Comp. Ex. 1 Comp. Ex. 2 Comp. Ex. 3 Comp. Ex. 4Interface with Non-alignment Non-alignment Non-alignment Non-alignmentNon-alignment ferro-magnetic very strong very strong strong weak verystrong layer (Hex) 17.4 × 10⁴ A/m 1.2 × 10⁴ A/m 0.79 × 10⁴ A/m 6.48 ×10⁴ A/m 8.37 × 10⁴ A/m Resistance 8.3% 5.5% 5.0% 8.0% 8.1% variationratio Features of With strong Non-aligned Anti- Unsatisfactory Best ofsamples PtMn non-aligned state is very ferromagnetic due to weakemploying state, bulk strong properties non- single-layered ideal advan-can hardly be alignment, PtMn, due to composition tageously, butobtained due although rather strong (Pt50-Mn50) anti- to strong idealbulk non-alignment is used for ferromagnetic non-alignment compositionand nearly 90% of more. properties and due to was used. ideal bulk canhardly be small a Pt composition. obtained due content. to too high a Ptcontent.

Table 1 shows the results of experiments performed on samples afterheat-treatment. With regards to “Interface with Ferromagnetic layer”,both Example 1 and Comparative Example 1 had a very strong state ofnon-alignment, whereas Comparative Examples 2 and 3 showed greatertendencies towards alignment. In Comparative Example 4, the non-alignedstate was not very strong.

In order to obtain a non-aligned interface structure, it is necessary toincrease the Pt content in the Pt—Mn alloy. In Example 1 and ComparativeExample 1, the Pt content of the antiferromagnetic layer contacting theinterface with the pinned magnetic layer was 58 at %, whereas the Ptcontent was smaller in each of the other samples, leading to theabove-described results.

With regards to “Hex” which represents the exchange coupling magneticfield, Example 1 showed a very large exchange coupling magnetic field of17.4×10⁴ A/m, while the Comparative Examples showed much smaller valuesof exchange coupling magnetic field. In Comparative Examples 3 and 4,the values of the exchange coupling magnetic fields were greater thanthose in Comparative Examples 1 and 2, but were much smaller than thatobtained with Example 1.

In order to obtain a large exchange coupling magnetic field, it isnecessary that the antiferromagnetic layer is formed of a Pt—Mn alloyhaving a composition that approximates an ideal composition forfacilitating transformation from a disordered lattice structure to anordered lattice structure upon heat-treatment. The ideal compositionherein refers to Pt₅₀Mn₅₀.

The use of the ideal composition alone is still insufficient. It is alsoimportant that the interface adjacent to the pinned magnetic layer isheld in a non-aligned state. An aligned state of the interface impedesproper transformation of the antiferromagnetic layer duringheat-treatment, due to the restraint force produced by the crystallinestructure of the pinned magnetic layer.

Example 1 alone simultaneously met these two conditions. Morespecifically, in Example 1, the interface between the firstantiferromagnetic layer and the pinned magnetic layer was held in thenon-aligned state in the as-deposited state before heat-treatment, whilethe second antiferromagnetic layer had the ideal composition. Incontrast, in Comparative example 1, antiferromagnetic properties couldhardly be obtained despite heat-treatment, because the compositiondeviated from the ideal composition due to too large a Pt content eventhough the interface adjacent to the pinned magnetic layer was held in anon-aligned state. In Comparative example 2, antiferromagneticproperties could hardly be obtained despite heat-treatment, because thecomposition deviated from the ideal composition due to too small a Ptcontent, and due to the aligned state at the interface adjacent to thepinned magnetic layer. In the case of Comparative Example 3, atransformation from disordered lattice structure to an ordered latticestructure could hardly occur despite heat-treatment, due to the alignedstate at the interface adjacent to the pinned magnetic layer, eventhough the ideal composition was employed. Comparative Example 4employed a composition approximating the ideal composition and had theinterface adjacent to the pinned magnetic layer which was comparativelyeasy to maintain in the non-aligned state. This Comparative exampleproduced an exchange coupling magnetic field which is the greatest ofall the other Comparative Examples but is still smaller than that ofExample 1, due to the large Pt content and due to the non-aligned statewhich is not very strong.

In accordance with the present invention, transformation from adisordered lattice structure into an ordered lattice structure caused byheat-treatment was properly performed without losing the non-alignedstate at the interface. This resulted from the facts that theantiferromagnetic layer as deposited had a first antiferromagnetic layer14 facing the interface adjacent to the pinned magnetic layer, acomposition was used in which it was easy to create the non-alignedstate, and a second antiferromagnetic layer 15 had a compositionapproximating the ideal composition and formed on the pinned magneticlayer with first antiferromagnetic layer 14 intervening therebetween.Thus, a greater exchange coupling magnetic field than those ofconventional devices was achieved. The data in the item “Resistancevariation ratio” also shows the superiority of Example 1 to theComparative examples.

Then, the relationship between the total film thickness of theantiferromagnetic layer and the exchange coupling magnetic field (Hex)was examined (see FIG. 17). The following two samples in theas-deposited state (prior to heat-treatment) were prepared. Thestructure of Example 2 was the same as that shown in FIG. 2, while thestructure of Comparative Example 5 was the same as that shown in FIG.20.

Example 2

The laminate structure was composed of the following layers, asmentioned from the bottom layer:

Underlying layer 6: Ta (50)/free magnetic layer 1:[Ni₈₀Fe₂₀(45)/Co(5)]/non-magnetic intermediate layer 2: Cu(25)/pinnedmagnetic layer 3: [Co(20)/Ru(8)/Co(15)]/first antiferromagnetic layer14: Pt₅₈Mn₄₂ (10)/second antiferromagnetic layer:Pt₅₀Mn₅₀(X-10)/protective layer 7: Ta(30)

Comparative Example 5

Underlying layer 6: Ta (50)/free magnetic layer 1:[Ni₈₀Fe₂₀(45)/Co(5)]/non-magnetic intermediate layer 2: Cu(25)/pinnedmagnetic layer 3: [Co(20)/Ru(8)/Co(15)]/antiferromagnetic layer 30:Pt₅₂Mn₄₈ (X)/protective layer 7: Ta(30)

Values in parentheses indicate layer thickness in Angstroms. Thesuffixes in the representations of Ni—Fe alloys and Pt—Mn alloysrepresent composition ratios in terms of at %.

In Example 2, the thickness of the first antiferromagnetic layer 14 wasfixed at 10 Å, while the thickness of the second antiferromagnetic layer15 was varied.

These samples were heat-treated and were subjected to measurement of theexchange coupling magnetic field (Hex). It will be seen that a greatertotal thickness of the Pt—Mn alloy layer provides a greater exchangecoupling magnetic field, both in Example 2 and Comparative Example 5, asshown in FIG. 17.

When the total thickness of the Pt—Mn layer was increased, (i.e., whenthe thickness of the second antiferromagnetic layer 15 was increased),Example 2 of the invention showed a drastic increase in the exchangecoupling magnetic field compared with that of Comparative Example 5. Anexchange coupling magnetic field as large as 7.9×10⁴ A/m or greater wasprovided when the total thickness reached and exceeded 80 Å.

An exchange coupling magnetic field of 7.9×10⁴ A/m or greater was alsoobtainable with Comparative Example 5 when the thickness of theantiferromagnetic layer exceeded about 120 Å, suggesting that a greaterthickness of antiferromagnetic layer 30 than in Example 2 was requiredfor achieving the same exchange coupling magnetic field as produced inExample 2.

This experiment also shows that when the antiferromagnetic layer 4 isformed by depositing two layers, first antiferromagnetic layer 14 andsecond antiferromagnetic layer 15, as in Example 2, the secondantiferromagnetic layer 15 that is formed by an antiferromagneticmaterial having a composition approximating the ideal composition forfacilitating transformation from a disordered lattice structure into anordered lattice structure should have a thickness greater than apredetermined thickness.

In accordance with the present invention, it is understood from theexperiment results shown in FIG. 17 that a large exchange couplingmagnetic field of 7.9×10⁴ A/m or greater is obtainable when the totalthickness of the antiferromagnetic layer is determined to be 80 Å orgreater. Since the thickness of first antiferromagnetic layer 14 is 10 Åin this case, the thickness of second antiferromagnetic layer 15 isdetermined to be 70 Å or greater.

Then, the relationship was examined between thickness of the firstantiferromagnetic layer and the exchange coupling magnetic field (Hex)in the structure in which the antiferromagnetic layer as deposited iscomposed of first antiferromagnetic layer 14 and secondantiferromagnetic layer 15 (FIG. 18). The laminate structure used inthis experiment was the same as that shown in FIG. 2. Example 3

The laminate structure was composed of the following layers, from thebottom layer up:

Underlying layer 6: Ta(50)

Free magnetic layer 1: [Ni₈₀Fe₂₀(45)/Co(5)]

Non-magnetic intermediate layer 2: Cu(25)

Pinned magnetic layer 3: [Co(20)/Ru(8)/Co(15)]

First antiferromagnetic layer 14: Pt₅₈Mn₄₂(X)

Second antiferromagnetic layer: Pt₅₀Mn₅₀(120-X)

Protective layer 7: Ta(30)

Values in parentheses indicate the layer thickness in Angstroms. Thesuffixes in the representations of Ni—Fe alloys and Pt—Mn alloysrepresent composition ratios in terms of at %.

A plurality of samples having different thicknesses of firstantiferromagnetic layer 14 were prepared and heat-treated, and theexchange coupling magnetic field was measured on each. From FIG. 18, itis understood that the exchange coupling magnetic field of 7.9×10⁴ A/mor greater was obtainable when the thickness X of the firstantiferromagnetic layer 14 ranged from 3 Å to 30 Å.

The first antiferromagnetic layer 14 had a large Pt content, in order tomaintain the required non-aligned state at the interface adjacent topinned magnetic layer 3. For instance, the Pt content was as large as 58at % in the Example. A composition having such a high Pt content is noteasy to transform from a disordered lattice structure to an orderedlattice structure when heat-treated. Therefore, such compositions canhardly exhibit antiferromagnetic properties, even though it effectivelymaintains the above-mentioned non-aligned state. Therefore, too large athickness of the first antiferromagnetic layer 14 increases the ratio ofthe region which is hard to transform. As will be clearly seen from theexperiment results shown in FIG. 18, this incurs a serious reduction inthe exchange coupling magnetic field.

In contrast, the thickness of the first antiferromagnetic layer 14ranging from 3 Å to 30 Å provides a large exchange coupling magneticfield, possibly for the reason that a diffusion of compositions takesplace between first antiferromagnetic layer 14 and secondantiferromagnetic layer 15 which is inherently easy to transform,throughout the whole thickness region of first antiferromagnetic layer14 when the thickness of first antiferromagnetic layer 14 falls withinthe above-specified range. This diffusion causes the Pt content to bedecreased in first antiferromagnetic layer 14 from that obtained in theas-deposited state, so that first antiferromagnetic layer 14 becomeseasier to transform and a large exchange coupling magnetic field isprovided.

Thus, in order to obtain a large exchange coupling magnetic field inaccordance with the present invention, it is necessary that secondantiferromagnetic layer 15-made of an antiferromagnetic materialapproximating an ideal composition which is easy to transform from adisordered lattice structure into an ordered lattice structure—isdeposited to have a thickness of 70 Å or greater, as explained abovewith reference to FIG. 17, and that first antiferromagnetic layer 14,which has a high Pt content to maintain the non-aligned state at theinterface adjacent to pinned magnetic layer—is deposited to have athickness ranging from 3 Å to 30 Å, as explained above with reference toFIG. 18.

Thus, the exchange coupling magnetic field of 7.9×10⁴ A/m or greater isobtainable when the thickness of the first antiferromagnetic layer 14 isset to be 3 Å or greater and the thickness of the secondantiferromagnetic layer 15 is set to be 70 Å or greater, thus providinga total thickness of antiferromagnetic layer 4 of 73 Å. Based on theresults of the experiment, in accordance with the present invention, thethickness of antiferromagnetic layer 4 after heat-treatment is set to be73 Å or greater.

Thus, in accordance with the present invention, the minimum thicknessrequired for antiferromagnetic layer 4 is 73 Å or greater, so that thethickness of the antiferromagnetic layer can be reduced compared withthat in conventional devices, thus meeting the demand for narrower gaps.

Next, the relationship was examined between the composition ratio of thefirst antiferromagnetic layer and the exchange coupling magnetic field(Hex) in the structure in which the antiferromagnetic layer as depositedis composed of first antiferromagnetic layer 14 and secondantiferromagnetic layer 15 (FIG. 19). The laminate structure used inthis experiment was the same as that shown in FIG. 2.

Example 4

The laminate structure was composed of the following layers, from thebottom layer up:

Underlying layer 6: Ta(50)

Free magnetic layer 1: [Ni₈₀Fe₂₀(45)/Co(5)]

Non-magnetic intermediate layer 2: Cu(25)

Pinned magnetic layer 3: [Co(20)/Ru(8)/Co(15)]

First antiferromagnetic layer 14: Pt_((x))Mn_((100-x))(10)

Second antiferromagnetic layer: Pt₅₀Mn₅₀(120-X)

Protective layer 7: Ta(30)

Values in parentheses indicate the layer thickness in Angstroms. Thesuffixes in the representations of Ni—Fe alloys and Pt—Mn alloysrepresent composition ratios in terms of at %.

A plurality of samples having different compositions of firstantiferromagnetic layer 14 were prepared and heat-treated, and theexchange coupling magnetic field (Hex) was measured on each. From FIG.19, it is understood that the exchange coupling magnetic field of7.9×10⁴ A/m or greater is obtainable when the Pt content of the firstantiferromagnetic layer 14 is not less than 53 at % and not greater than65 at %.

A Pt content of first antiferromagnetic layer 14 ranging from 53 at % to65 at % can adequately create a non-aligned state at the interfacebetween first antiferromagnetic layer 14 and pinned magnetic layer 3.This is the reason why the large exchange coupling magnetic field isobtained.

It is understood, however, that the exchange coupling magnetic fieldstarts to decrease when the Pt content exceeds 65 at %. It is consideredthat, when the first antiferromagnetic layer 14 as deposited containssuch a large amount of Pt, the Pt content in the first antiferromagneticlayer is not decreased to such a level as to enable a propertransformation in the first antiferromagnetic layer 14, despite anydiffusion of compositions between first antiferromagnetic layer 14 andsecond antiferromagnetic layer 15 caused upon heat-treatment. As aresult, the exchange coupling magnetic field is reduced.

It is understood that a large exchange coupling magnetic field,specifically 11.85×10⁴ A/m or greater, is obtainable when the Pt contentis determined to be not less than 55 at % and not greater than 60 at %.A Pt content less than 53 at % causes a reduction in the exchangecoupling magnetic field. Such a small Pt content makes the latticeconstant of antiferromagnetic layer 4 approach that of pinned magneticlayer 3, so as to make it difficult to create the required non-alignedstate.

Next, in accordance with the present invention, an experiment wasconducted using samples prepared in Example 5, in which theantiferromagnetic layer 4 was deposited by a different method, andexchange coupling magnetic fields (Hex) after heat-treatment.

The materials and thicknesses of the layers other than antiferromagneticlayer 4 were the same as in Examples 1 to 3. In this experiment, theantiferromagnetic layer 4 in each sample was deposited on pinnedmagnetic layer 3 using a target formed of a Pt—Mn alloy, while thesputtering gas pressure was progressively changed from low to high. Ameasurement of the composition ratio along the thickness ofantiferromagnetic layer 4 proved that a composition Pt₅₈Mn₄₂ wasdeveloped at the region near the interface adjacent to pinned magneticlayer 3, and that the Pt content progressively decreased in thedirection away from the interface to develop a composition Pt₄₈Mn₅₂ inthe region near the side of antiferromagnetic layer 4 opposite to theinterface.

A laminate structure having an antiferromagnetic layer 30 was preparedin Comparative Example 5, the whole structure of antiferromagnetic layer30 having a composition Pt₅₂Mn₄₈. Materials and thicknesses of thelayers other than antiferromagnetic layer 30 were the same as inComparative Examples 1 to 4.

Samples deposited in accordance with Example 5 and Comparative Example 5were subjected to heat-treatment and subsequent measurement of theexchange coupling magnetic field. The results are shown in Table 2. Theheat-treatment was conducted for more than 2 hours at temperatures notlower than 200° C.

TABLE 2 Example 5 Comp. Ex. 5 Interface Non-alignment very strongNon-alignment very strong with ferro- magnetic layer (Hex) 16.43 × 10⁴A/m 8.37 × 10⁴ A/m Resistance 8.4% 8.1% variation ratio Features ofComposition modulation was The non-aligned state was PtMn effected whilemaintaining held rather strong, and a very strong non-alignedcomposition approximates state, so that most of bulk ideal composition.film was constituted by Best composition among composition approximatingsamples of single-layered the ideal composition. type.

With regards to “Interface with ferromagnetic layer,” the non-alignedstate in Example 5 was strongly held in the interface structure betweenantiferromagnetic layer 4 and pinned magnetic layer 3. In ComparativeExample 5, the non-aligned state was not as strong as in Example 5,although this Comparative Example employed a composition whichfacilitated creation of the non-aligned state.

There was no significant difference in the resistance variation ratio(ΔMR) between Example 5 and Comparative Example 5.

A major difference between Example 5 and Comparative example 5 is thatthe former exhibited an exchange coupling magnetic field (Hex) two timesas large as that of the latter.

Example 5 showed such a large exchange coupling magnetic field due toproper transformation of the antiferromagnetic layer 4. This wasafforded by the high Pt content (Pt₅₈Mn₄₂) of antiferromagnetic layer 4at the interface adjacent to the pinned magnetic layer. The non-alignedstate is properly maintained at that interface, and by the compositionmodulation in the thicknesswise direction of antiferromagnetic layer 4,executed such that most of antiferromagnetic layer 4 was constituted bycompositions approximating the ideal composition for facilitatingtransformation from a disordered lattice structure into a latticestructure upon heat-treatment.

Next, in accordance with the invention, samples were prepared in Example6 in which antiferromagnetic layer 4 of a so-called dual-spin valve typemagnetoresistive sensor was deposited to have a laminate structurecomposed of a first antiferromagnetic layer 14 and a secondantiferromagnetic layer 15. Samples were also prepared in ComparativeExample 6 in which the antiferromagnetic layer was composed of a singlelayer. Exchange coupling magnetic fields were measured on these samples.

Example 6

The laminate structure was composed of the following layers, asmentioned from the bottom layer:

Second antiferromagnetic layer: Pt₅₀Mn₅₀(83)/first antiferromagneticlayer 14: Pt₅₈Mn₄₂ (7)/pinned magnetic layer 3:[Co(15)/Ru(8)/Co(20)]/non-magnetic intermediate layer 2: Cu(22)/freemagnetic layer 1: Co (20)/non-magnetic intermediate layer 2:Cu(22)/pinned magnetic layer 3: [Co(20)/Ru(8)/Co(15)]/firstantiferromagnetic layer 14: Pts₈Mn₄₂ (7)/second antiferromagnetic layer:Pt₅₀Mn₅₀(83)/protective layer 7: Ta(10)

Comparative Example 6

The laminate structure had the following layers as mentioned from thebottom:

Antiferromagnetic layer 30: Pt₅₀Mn₅₀(90)/pinned magnetic layer 3:[Co(15)/Ru(8)/Co(20)]/non-magnetic intermediate layer 2: Cu(22)/freemagnetic layer 1: Co (20)/non-magnetic intermediate layer 2:Cu(22)/pinned magnetic layer 3: [Co(20)/Ru(8)/Co(15)]/antiferromagneticlayer 30:Pt₅₀Mn₅₀(90)/protective layer 7: Ta(10)

Values in parentheses indicate the layer thickness in Angstroms. Thesuffixes in the representations of Ni—Fe alloys and Pt—Mn alloysrepresent composition ratios in terms of at %.

The samples of Example 6 and Comparative Example 6 as deposited weresubjected to heat-treatment and then to measurement of the exchangecoupling magnetic field. The results are shown in Table 3. Theheat-treatment was conducted for more than 2 hours at temperatures notlower than 200° C.

TABLE 3 Example 6 Comp. Ex. 6 Interface with Non-alignment veryNon-alignment rather ferro-magnetic strong strong layer (Hex) 15.96 ×10⁴ A/m 10.59 × 10⁴ A/m Resistance 140% 13.4% variation ratio Featuresof With strong non-aligned Non-aligned state is PtMn state, bulk idealheld rather strong, and composition (Pt50-Mn50) composition is used for90% of approximates bulk ideal more. composition. Best composition amongsamples of single- layered type.

With regards to “Interface with ferromagnetic layer,” the non-alignedstate in Example 6 was strongly held in the interface structure betweenantiferromagnetic layer 4 and pinned magnetic layer 3. In ComparativeExample 6, the non-aligned state was not as strong as in Example 6,although this Comparative Example employed a composition whichfacilitated creation of the non-aligned state.

There was no significant difference in the resistance variation ratio(AMR) between Example 6 and Comparative Example 6.

A major difference between Example 6 and Comparative example 6 is thatthe former exhibited an exchange coupling magnetic field (Hex) muchgreater than that of the latter.

Example 6 showed such a large exchange coupling magnetic field due tothe fact that the transformation from the disordered lattice structureinto the ordered lattice structure was properly effected byheat-treatment, while the non-aligned state was maintained. This, inturn, is due to the fact that the interface adjacent to the pinnedmagnetic layer was held in the non-aligned state due to the formation ofthe first antiferromagnetic layer 14 and because secondantiferromagnetic layer 15, having an ideal composition for facilitatingtransformation upon heat-treatment, was formed on pinned magnetic layer3 through the first antiferromagnetic layer.

Next, in accordance with the present invention, four types of laminatestructures each having a seed layer 22 explained above with reference toFIG. 4 were prepared, including two types of samples (Example 7 andExample 8) in which the interface adjacent to the seed layer was held ina non-aligned state, and two types of samples (Comparative Example 7 andComparative Example 8) in which the interface adjacent to seed layer 22was held in an aligned state. These samples were subjected toheat-treatment and subsequent measurement of the exchange couplingmagnetic field (Hex) and resistance variation ratio (ΔMR). Thestructures of Examples 7 and 8 were the same as that shown in FIG. 8,while the structures of Comparative Examples 7 and 8 were the same asthat shown in FIG. 21.

Example 7

The laminate structure had the following layers, as mentioned from thebottom:

Underlying layer 6: Ta(50)/seed layer 22: Ni₈₀Fe₂₀(30)/antiferromagneticlayer 4[third antiferromagnetic layer 25: Pt₅₈Mn₄₂(10)/secondantiferromagnetic layer 24: Pt₅₀Mn₅₀(100)/first antiferromagnetic layer23: Pt₅₈Mn₄₂(10)]/pinned magnetic layer3[Co(15)/Ru(8)/Co(20)]/non-magnetic intermediate layer 2: Cu(22)/freemagnetic layer 1[Co(5)/Ni₈₀Fe₂₀(45)]/protective layer 7: Ta(30)

Example 8

The laminate structure had the following layers, as mentioned from thebottom:

Underlying layer 6: Ta(50)/seed layer 22:Ni₆₀Fe₁₀Cr₃₀(30)/antiferromagnetic layer 4 [third antiferromagneticlayer 25: Pt₅₈Mn₄₂(10)/second antiferromagnetic layer 24:Pt₅₀Mn₅₀(100)/first antiferromagnetic layer 23: Pt₅₈Mn₄₂(10)]/pinnedmagnetic layer 3 [Co(15)/Ru(8)/Co(20)]/non-magnetic intermediate layer2: Cu(22)/free magnetic layer 1 [Co(5)/Ni₈₀Fe₂₀(45)]/protective layer 7:Ta(30)

Comparative Example 7

The laminate structure had the following layers, as mentioned from thebottom:

Underlying layer 6: Ta(50)/seed layer 22: Ni₈₀Fe₂₀(30)/antiferromagneticlayer 31: Pt₅₀Mn₅₀(120)/pinned magnetic layer3[Co(15)/Ru(8)/Co(20)]/non-magnetic intermediate layer 2: Cu(22)/freemagnetic layer 1 [Co(5)/Ni₈₀Fe₂₀(45)]/protective layer 7: Ta(30)

Comparative Example 8

The laminate structure had the following layers, as mentioned from thebottom:

Underlying layer 6: Ta(50)/seed layer 22:Ni₆₀Fe₁₀Cr₃₀(30)/antiferromagnetic layer 31: Pt₅₀Mn₅₀(120)/pinnedmagnetic layer 3 [Co(15)/Ru(8)/Co(20)]/non-magnetic intermediate layer2: Cu(22)/free magnetic layer 1 [Co(5)/Ni₈₀Fe₂₀(45)]/protective layer 7:Ta(30)

Values in parentheses indicate layer thickness in Angstroms. Thesuffixes in the representations of Ni—Fe alloys and Pt—Mn alloysrepresent composition ratios in terms of at %.

These samples formed to have the above-mentioned structures wereheat-treated, and the exchange coupling magnetic field (Hex) andresistance variation ratio (ΔMR) were measured. The results are shown inTable 4. The heat-treatment was conducted for more than 2 hours attemperatures not lower than 200° C.

TABLE 4 Example 7 Example 8 Comp. Ex. 7 Comp. Ex. 8 Interface with seedNon-alignment Non-alignment very Almost aligned Almost aligned layervery strong strong Saturation magnetic 0.9 T Non-magnetic 0.9 TNon-magnetic field of seed layer specific resistance 25 μΩ · cm 160 μΩ ·cm 25 μΩ · cm 160 μΩ · cm of seed layer Crystalline Mostly face- Mostlyface- Mostly face- Mostly face- structure of seed centered cubescentered cubes with centered cubes with centered cubes with layer withstrong (111) strong (111) plane strong (111) plane strong (111) planeplane orientation orientation orientation orientation Interface withNon-alignment Non-alignment very Almost aligned Almost alignedferro-magnetic very strong strong layer (Hex) 18.2 × 10⁴ A/m 18.5 × 10⁴A/m 6 × 10⁴ A/m 6.5 × 10⁴ A/m Resistance 7.8% 10.29% 8.1% 10.3%variation ratio Role played by seed Seed layer is composed mainly offace-centered cubic structure with the layer densest (111) planestrongly aligned, so that layers from Pt to free layer have ratherstrong (111) plane orientation and, accordingly, greater crystal grains,resulting in large resistance variation ratio. Alignment between seedlayer and PtMn, however, makes it difficult to obtain large Hex on onehand, but on the other hand, significantly enhances the (111) planes oflayers down to the free layer, resulting in greater crystal grain sizeand consequently greater resistance variation ratio. In order tosimultaneously meet the requirements for greater Hex and greaterresistance variation ratio, it is preferred that the (111) planeorientations are enhanced in the layers from the PtMn layer to the freelayer, while maintaining a non-aligned state between the seed layer andthe PtMn layer, as in Example 8. Features of PtMn Bulk ideal Bulk idealInsufficient due to insufficient due to composition (Pt50- composition(Pt50- almost-aligned almost-aligned Mn 50) used in Mn 50) used in thestate, although the state, although the the region around region aroundcomposition is composition is central region, central region, idealideal while maintaining while maintaining very strongly very stronglynon- non-aligned state aligned state Feature of Variation ratioVariation ratio Variation ratio not Variation ratio resistance not largebecause large because of large because of large because of variationratio of small specific large specific small specific large specificresistance of resistance of seed resistance of seed resistance of seedseed layer layer layer layer

As shown in Table 4, the same “Role of seed layer” was applicable toExamples 7 and 8, and Comparative Examples 7 and 8. The seed layer 22 inaccordance with the present invention is primarily constituted by aface-centered cubic structure, with the (111) planes preferentiallyoriented in the direction parallel to the interface. Therefore, thelayers formed on seed layer 22, from the antiferromagnetic layer to freemagnetic layer 1, also have their (111) planes preferentially orientedin the direction parallel to the interfaces, thus causing greatercrystal grains. For these reasons, large resistance variation ratioswere obtained in all samples, as will be seen from FIG. 4.

Example 8 showed a greater resistance variation ratio than Example 7,and Comparative Example 8 showed a greater resistance variation ratiothan Comparative Example 7. In Example 7 and Comparative Example 7, theseed layer 22 formed of Ni₈₀Fe₂₀ alloy had a low specific resistance,whereas in Example 8 and Comparative Example 8 the seed layer 22containing non-magnetic Cr and having a composition Ni₆₀Fe₁₀ Cr₃₀ had ahigh specific resistance.

In example 7 and Comparative Example 7, the sense current shunted intoseed layer 22 due to the low specific resistance, whereas, in Example 8and Comparative Example 8, such shunting did not take place. As aresult, greater resistance variation ratios were obtained in Example 8and Comparative Example 8 than in Example 7 and Comparative Example 7.

Referring now to the exchange coupling magnetic field, it is understoodthat Examples 7 and 8 showed much greater exchange coupling magneticfields than those obtained in Comparative Examples 7 and 8. This isbecause in Examples 7 and 8, the interface adjacent to seed layer 22 andthe interface adjacent to pinned magnetic layer 3 were held in thenon-aligned state, by virtue of the presence of third antiferromagneticlayer 25 and first antiferromagnetic layer 23. In contrast, inComparative Examples 7 and 8, transformation from the disordered latticestructure to the ordered lattice structure could hardly occur due to thealigned state at the interface adjacent to the seed layer and at theinterface adjacent to pinned magnetic layer 3, even thoughantiferromagnetic layer 31 had an ideal composition for facilitatingtransformation from a disordered lattice structure to an ordered latticestructure upon heat-treatment. Thus, smaller values of the exchangecoupling magnetic field resulted.

From the results of this experiment, it is understood that therequirements for high resistance variation ratio and exchange couplingmagnetic field are satisfied when the following conditions are met.Namely, a large resistance variation ratio can be obtained when a seedlayer 22 made of a non-magnetic material having a large specificresistance is formed on the side of the antiferromagnetic layer oppositeto the interface adjacent pinned magnetic layer 3. At the same time, itis preferred that antiferromagnetic layer 4 is formed by depositingthree layers, wherein first antiferromagnetic layer 23 contacting pinnedmagnetic layer 3, and third antiferromagnetic layer 25 contacting seedlayer 22, are made to have a large Pt content so that the non-alignedstate is maintained at the interfaces adjacent to pinned magnetic layer3 and seed layer 22. The second antiferromagnetic layer 24 formedbetween first and second antiferromagnetic layers 23 and 25 is formed tohave an ideal composition that is easy to transform from a disorderedlattice structure into an ordered lattice structure upon heat-treatment.By using this antiferromagnetic layer, it is possible to enhance theexchange coupling magnetic field (Hex).

As in the case of the experiment results shown in FIGS. 18 and 19, thethicknesses of the first antiferromagnetic layer 23 and the thirdantiferromagnetic layer 25 are preferably not less than 3 Å and notgreater than 30 Å. The composition ratios are preferably such that thePt content is not less than 53 at % and not greater than 65 at %. Thethickness of second antiferromagnetic layer 24 is preferably 70 Å orgreater, as in the case of the experiment results shown in FIG. 17.

As has been described in detail above, the process for producing anexchange coupling film in accordance with the present inventionpreferably involves forming a seed layer on the side of theantiferromagnetic layer opposite the interface with the pinned magneticlayer, wherein the seed layer has a crystalline structure primarilyconstituted by face-centered cubic crystals having (111) planespreferentially oriented in a direction parallel to the interface. Thispermits the (111) planes of the antiferromagnetic layer and the pinnedmagnetic layer to be easily oriented preferentially in a directionparallel to the above-mentioned interface.

Further, in accordance with the present invention, the interface betweenthe seed layer and the antiferromagnetic layer is held in a non-alignedstate. This enables the antiferromagnetic layer to be properlytransformed from a disordered lattice structure into an ordered latticestructure upon heat-treatment, thereby providing a large exchangecoupling magnetic field.

In accordance with the present invention, the antiferromagnetic layer isdeposited while the sputtering gas pressure is progressively changed.Alternatively, the antiferromagnetic layer is deposited to have threelayers including first through third antiferromagnetic layers. The firstand third antiferromagnetic layers have a larger composition ratio ofthe element X or the elements X+X′ than the second antiferromagneticlayer. As a result, the antiferromagnetic layer is properly transformedupon heat-treatment without being restrained by the crystallinestructure of the seed layer. A greater exchange coupling magnetic fieldthan heretorfore is thus obtained.

By using the above-described exchange coupling film in amagnetoresistive sensor, it is possible to cause the (111) planes of thelayers of the magnetoresistive sensor to be preferentially oriented,allowing growth of large crystal grains. As a result, a greater ratio ofresistance variation is achieved. At the same time, the greater exchangecoupling magnetic field achieved with the present invention alsocontributes to the increase of the resistance variation ratio.

Preferably, the seed layer is non-magnetic so that the shunting of thesense current to the seed layer is suppressed, and a further increase inresistance variation ratio is achieved.

1. A method of producing an exchange coupling film comprising anantiferromagnetic layer, a ferromagnetic layer, and a seed layercomprising a (111) plane of face-centered cubic crystal, which seedlayer contacts said antiferromagnetic layer at an interface therebetweenon a side opposite to said ferromagnetic layer, said method comprising:forming said ferromagnetic layer such that said ferromagnetic layercontacts said antiferromagnetic layer at an interface therebetween;forming said seed layer such that said (111) plane of face-centeredcubic crystal is preferentially oriented in a direction parallel to saidinterface between said seed layer and said antiferromagnetic layer,thereby creating a difference lattice constant between saidantiferromagnetic layer and said seed layer at at-least a part of saidinterface between said antiferromagnetic layer and said seed layer; andheat treating the so formed ferromagnetic layer, antiferromagneticlayer, and seed layer composite structure such that an exchange couplingmagnetic field is developed at said interface between saidantiferromagnetic layer and said ferromagnetic layer.
 2. The method ofclaim 1, wherein a non-aligned state is created at at least a part ofsaid interface between said antiferromagnetic layer and said seed layer.3. The method of claim 1, wherein said antiferromagnetic layer comprisesan element X and Mn, wherein X is selected from the group consisting ofPt, Pd, Ir, Rh, Ru, Os, and combinations thereof.
 4. The method of claim1, wherein said antiferromagnetic layer comprises an element X, anelement X′ and Mn, wherein X is selected from the group consisting ofPt, Pd, Ir, Rh, Ru, Os, and combinations thereof, and X′ is selectedfrom the group consisting of Ne, Ar, Kr, Xe, Be, B, C, N, Mg, Al, Si, P,Ti, V, Cr, Fe, Co, Ni, Cu, Zn, Ga, Ge, Zr, Nb, Mo, Ag, Cd, Sn, Hf, Ta,W, Re, Au, Pb, a rare earth element, and combinations thereof.
 5. Themethod of claim 4, wherein said element X′ of said antiferromagneticlayer is futher selected from the subgroup of the group listed in claim7, the subgroup consisting of an element which invades interstices of aspace lattice composed of said element X and said Mn, and an elementwhich substitutes for a portion of lattice points of a crystallinelattice constituted by said Mn and said element X.
 6. The method ofclaim 1, wherein said antiferromagnetic layer and said ferromagneticlayer have different lattice constants at at least a part of saidinterface therebetween.
 7. The method of claim 1, wherein a non-alignedstate is created at at least a part of said interface between saidantiferromagnetic layer and said ferromagnetic layer.
 8. The method ofclaim 1, wherein said seed layer comprises an alloy selected from thegroup consisting of a Ni—Fe alloy and a Ni—Fe—Y alloy, wherein Y isselected from the group consisting of Cr, Rh, Ta, Hf, Nb, Zr, Ti, andcombinations thereof.
 9. The method of claim 1, wherein said seed layeris non-magnetic.
 10. The method of claim 1, wherein said exchangecoupling film further comprises an underlying layer, which comprises anelement selected from the group consisting of Ta, Hf, Nb, Zr, Ti, Mo, W,and combinations thereof, and wherein said seed layer is adjacent tosaid underlying layer.
 11. A method of producing a magnetoresistivesensor, the method comprising: forming an antiferromagnetic layer;forming a seed layer, such that a (111) plane of face-centered cubiccrystal of said seed layer is oriented in a direction parallel to aninterface between said seed layer and said antiferromacinetic layer,thereby creating a difference in lattice constant between saidantiferromacinetic layer and said seed layer at at least a part of saidinterface between said antiferromagnetic layer and said seed layer; andforming a pinned magnetic layer contacting said antiferromagnetic layerat an interface therebetween; heat treating the so formed pinnedmagnetic layer, antiferromagnetic layer, and seed layer compositestructure such that an exchange coupling magnetic field is developed atsaid interface between said antiferromagnetic layer and said pinnedmagnetic layer. forming a non-magnetic intermediate layer between saidpinned magnetic layer and a free magnetic layer; and forming a biaslayer which aligns a direction of magnetization of said free magneticlayer in a direction that intersects said direction of magnetization ofsaid pinned magnetic layer.
 12. A method of producing a magnetoresistivesensor, the method comprising: forming an antiferromagnetic layer, aseed layer contacting said antiferromagnetic layer at an interfacetherebetween, a pinned magnetic layer contacting said antiferromagneticlayer at an interface therebetween which has a direction ofmagnetization fixed by an exchange anisotropic magnetic field with saidantiferromagnetic layer; forming a free magnetic layer having an upperside and a lower side; forming a non-magnetic intermediate layer betweensaid pinned magnetic layer and said free magnetic layer; forming anantiferromagnetic exchange bias layer formed on either said upper sideor said lower side of said free magnetic layer, said antiferromagneticexchange bias layer comprising a plurality of portions spaced from eachother in a track width direction, wherein a (111) plane of face-centeredcubic crystal of said non-magnetic layer is oriented in a directionparallel to an interface between said free magnetic layer and saidnon-magnetic layer, thereby creating a difference in lattice constantbetween said non-magnetic layer and said free magnetic layer at at leasta part of said interface between said non-magnetic layer and said freemagnetic layer; and heat treating the so formed free magnetic layer,antiferromagnetic exchange bias layer, and non-magnetic layer compositestructure such that an exchange coupling magnetic field is developed atsaid interface between with said antiferromagnetic exchange bias layerand said free magnetic layer.
 13. A method of producing amagnetoresistive sensor, the method comprising; forming a seed layer; afirst antiferromagnetic layer overlying said seed layer; a first pinnedmagnetic layer overlying said first antiferromagnetic layer; forming afirst non-magnetic layer overlying said first pinned magnetic layer; afree magnetic layer overlying said first non-magnetic layer, said freemagnetic layer having an upper side and a lower side; forming a secondnon-magnetic layer overlying said free magnetic layer; a second pinnedmagnetic layer overlying said second non-magnetic layer; and a secondantiferromagnetic layer overlying said second pinned magnetic layer,wherein a (111) plane of face-centered cubic crystal of at least one ofsaid seed layer and said second non-magnetic layer is oriented in adirection parallel to an interface between at least one of said firstantiferromagnetic layer and said first pinned layer and said secondpinned layer and second antiferromagnetic layer, thereby creating adifference in lattice constant between at least one of said firstantiferromagnetic layer and said first pinned layer, and said secondpinned layer and second antiferromagnetic layer at at least a part of atleast one of said interface between said first antiferromagnetic layerand said first pinned layer and said second pinned layer and secondantiferromagnetic layer; and heat treating at least one of the so formedsaid first pinned layer, first antiferromagnetic layer, and seed layer,and said second antiferromagnetic layer, second pinned layer, and secondnon-magnetic layer composite structure such that an exchange couplingmagnetic field is developed at at least one of said interface betweenwith said first antiferromagnetic exchange bias layer and said firstpinned magnetic layer, and said second antiferromagnetic layer andsecond pinned layer; and forming a bias layer which aligns a directionof magnetization of said free magnetic layer to a direction thatintersects said directions of said first and said second pinned magneticlayers.
 14. A method of producing a magnetoresistive sensor, the methodcomprising: forming a magnetoresistive layer having an upper side and alower side and a soft magnetic layer, said magnetoresistive layer andsaid soft magnetic layer being superposed through the intermediacy of anon-magnetic layer; forming an antiferromagnetic layer on said upperside or said lower side of said magnetoresistive layer, saidantiferromagnetic layer comprising a plurality of portions spaced apartin a track width direction; and forming a seed layer contacting saidantiferromagnetic layer, such that a (111) plane of face-centered cubiccrystal of said seed layer is oriented in a direction parallel to aninterface between said seed layer and said antiferromagnetic layer,thereby creating a difference in lattice constant between saidantiferromagnetic layer and said seed layer at at least a part of saidinterface between said antiferromagnetic layer and said seed layer; andheat treating the so formed magnetoresistive layer, antiferromagneticlayer, and seed layer composite structure such that an exchange couplingmagnetic field is developed at said interface between saidantiferromagnetic layer and said magnetoresistive layer.